(12) United States Patent (10) Patent No.: US 9,575,037 B2 Acharya Et Al

USOO9575037B2

(12) United States Patent (10) Patent No.: US 9,575,037 B2 Acharya et al. (45) Date of Patent: Feb. 21, 2017

(54) DETECTION OF GAS-PHASE ANALYTES G01N 33/0037: G01N 33/0044; Y10T USING LIQUID CRYSTALS 436/17; Y10T 436/173076; Y10T 436/177692; Y1OT 436/18: Y10T (71) Applicant: Platypus Technologies, LLC, Madison, 436/184; Y10T 436/20: Y10T WI (US) 436/200833; Y10T 436/202499; Y10T 436/25875 (72) Inventors: Bharat R. Acharya, Madison, WI (US); Kurt A. Kupcho, Madison, WI USPC ...... 436/106, 110, 116, 118, 121, 127, 128, (US); Bart A. Grinwald, Verona, WI 436/130, 164, 165, 167, 181; 422/50, (US); Sheila E. Robinson, Fitchburg, 422/68.1, 82.05, 82.09, 83, 88 WI (US): Avijit Sen, Madison, WI See application file for complete search history. (US); Nicholas Abbott, Madison, WI (US) (56) References Cited U.S. PATENT DOCUMENTS (73) Assignee: PLATYPUS TECHNOLOGIES, LLC, Madison, WI (US) 4,772,376 A * 9/1988 Yukawa ...... GON 27,417 204,410 (*) Notice: Subject to any disclaimer, the term of this 6,284, 197 B1 9, 2001 Abbott et al. patent is extended or adjusted under 35 6,858,423 B1* 2/2005 Abbott ...... B82Y 15.00 435/287.2 U.S.C. 154(b) by 0 days. 7,135,143 B2 11/2006 Abbott et al. 2010/0093.096 A1* 4/2010 Acharya ...... B82Y 3O/OO (21) Appl. No.: 14/774,964 436/4 2012/0288951 A1 11/2012 Acharya et al. (22) PCT Fed: Mar. 12, 2014 FOREIGN PATENT DOCUMENTS (86) PCT No.: PCT/US2O14/O24735 WO 99.63329 12/1999 S 371 (c)(1), WO O1? 61325 8, 2001 (2) Date: Sep. 11, 2015 WO O1? 61357 8, 2001 PCT Pub. No.: WO2O14/165196 (87) OTHER PUBLICATIONS PCT Pub. Date: Oct. 9, 2014 Jerome et al. "Anchoring of nematic liquid crystals on mica in the (65) Prior Publication Data presence of volatile molecules” Physical Review E., 1993, vol. 48, No. 6, pp. 4556-4571. US 2016/OO18371 A1 Jan. 21, 2016 Shah et al. “Principles for measurement of chemical exposure based on recognition-driven anchoring transitions in liquid crystals' Sci Related U.S. Application Data ence, 2001, vol. 293, pp. 1296-1299. (60) Provisional application No. 61/779,569, filed on Mar. Janzen et al. "Colorimetric sensor arrays for volatile organic com 13, 2013, provisional application No. 61/779,561, pounds' Analytical Chemistry, 2006, vol. 78, No. 11, pp. 3591 filed on Mar. 13, 2013. 3600. (51) Int. C. * cited by examiner GOIN 33/00 (2006.01) GOIN 33/497 (2006.01) Primary Examiner — Maureen Wallenhorst B82. 30/00 (2011.01) (74) Attorney, Agent, or Firm — Casimir Jones S.C. (52) U.S. C. CPC ...... G0IN 33/0004 (2013.01); B82Y 30/00 (57) ABSTRACT (2013.01); G0IN 33/0037 (2013.01); G0IN Provided herein is technology relating to detecting gaseous 33/0044 (2013.01); G0IN 33/497 (2013.01); analytes and particularly, but not exclusively, to devices and Y10T 436/177692 (2015.01); Y10T 436/184 methods related to detecting gaseous analytes by monitoring (2015.01); Y10T 436/202499 (2015.01); Y10T changes in liquid crystals upon exposure to the gaseous 436/25875 (2015.01) analytes. (58) Field of Classification Search CPC. B82Y 30/00; G01N 33/0004: G01N 33/497; 19 Claims, 65 Drawing Sheets U.S. Patent Feb. 21, 2017 Sheet 1 of 65 US 9,575,037 B2

FIG. 1A

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FIG. 1C

U.S. Patent Feb. 21, 2017 Sheet 2 of 65 US 9,575,037 B2

FIG. 2A

U.S. Patent Feb. 21, 2017 Sheet 3 of 65 US 9,575,037 B2

FIG. 3

SSS

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FIG. 4A

FIG. 4B

U.S. Patent Feb. 21, 2017 Sheet S of 65 US 9,575,037 B2

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FIG. 12

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FIG. 13

O 2 4 6 8 Exposure Time (min) U.S. Patent Feb. 21, 2017 Sheet 15 of 65 US 9,575,037 B2

FIG. 14

1 2 3 4 5 6 Exposure Time (hrs) U.S. Patent Feb. 21, 2017 Sheet 16 of 65 US 9,575,037 B2

FIG. 15

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U.S. Patent Feb. 21, 2017 Sheet 30 of 65 US 9,575,037 B2

FIG. 29

U.S. Patent Feb. 21, 2017 Sheet 31 of 65 US 9,575,037 B2

FIG 30 U.S. Patent Feb. 21, 2017 Sheet 32 of 65 US 9,575,037 B2

FIG. 31

0 ppb 40 ppb 10 ppb 50 ppb 15 ppb 60 ppb 20 ppb 70 ppb

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U.S. Patent Feb. 21, 2017 Sheet 47 of 65 US 9,575,037 B2

U.S. Patent Feb. 21, 2017 Sheet 48 of 65 US 9,575,037 B2

FIG. 47

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Docosane (C) Tetracosane (C) U.S. Patent Feb. 21, 2017 Sheet 49 of 65 US 9,575,037 B2

U.S. Patent Feb. 21, 2017 Sheet 50 of 65 US 9,575,037 B2

U.S. Patent Feb. 21, 2017 Sheet 51 of 65 US 9,575,037 B2

U.S. Patent Feb. 21, 2017 Sheet 52 of 65 US 9,575,037 B2

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U.S. Patent Feb. 21, 2017 Sheet 59 of 65 US 9,575,037 B2

FIG. 58

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U.S. Patent Feb. 21, 2017 Sheet 61 of 65 US 9,575,037 B2

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U.S. Patent Feb. 21, 2017 Sheet 62 of 65 US 9,575,037 B2

FIG. 61

Before exposure After exposure U.S. Patent Feb. 21, 2017 Sheet 63 of 65 US 9,575,037 B2

U.S. Patent Feb. 21, 2017 Sheet 64 of 65 US 9,575,037 B2

U.S. Patent Feb. 21, 2017 Sheet 65 of 65 US 9,575,037 B2

s US 9,575,037 B2 1. 2 DETECTION OF GAS-PHASE ANALYTES For example, Volatile organic compounds (VOCs) are a USING LIQUID CRYSTALS class of widely used organic chemicals that present signifi cant long-term and short-term health risks. These com CROSS-REFERENCE TO RELATED pounds have a high vapor pressure in ambient conditions APPLICATIONS and thus are readily outgassed from products that contain them. For example, VOCs are present in a wide array of This application is a 371 U.S. National Phase Entry of products Such as paints and lacquers, paint strippers, clean pending International Application No. PCT/US2014/ ing Supplies, pesticides, building materials and furnishings, 024735, filed Mar. 12, 2014, which claims priority to U.S. office equipment Such as copiers and printers, correction 10 fluids and carbonless copy paper, graphics and craft mate Prov. Pat. Appl. Ser. No. 61/779,561, filed Mar. 13, 2013, rials including glues and adhesives, permanent markers, and and U.S. Prov. Pat. Appl. Ser. No. 61/779,569, filed Mar. 13, photographic solutions. Consequently, many people are 2013, the contents of which are incorporated herein by exposed to VOCs daily. reference in their entireties. To protect these people from dangerous exposure to 15 hazardous environments, there is a need for inexpensive FIELD OF TECHNOLOGY devices that measure the concentration of these harmful compounds. Existing devices for measurement of VOCs rely Provided herein is technology relating to detecting vola mainly on the photoionization detector-based technology tile organic compounds and gaseous analytes and particu and require high power to operate and are expensive for larly, but not exclusively, to devices and methods related to wide applications. The devices based on colorimetric detec detecting volatile organic compounds and gaseous analytes tion of VOCs, on the other hand, are ambiguous and do not by measuring changes in the physical properties of liquid provide quantitative measurement. Therefore, there is an crystals upon exposure to the Volatile organic compounds unmet need for a simple technology that enables develop and gaseous analytes. ment of an inexpensive sensor device for quantitative detec 25 tion of VOCs for a number of applications including BACKGROUND HazMat/Homeland Security, industrial hygiene, indoor air quality, military applications, and biomedical applications. The types and concentrations of synthetic chemicals that In addition to applications related to monitoring exposure are in our environment are of greater concern to government, to dangerous gas-phase chemicals and protecting the health businesses, and Society in general than in any time in history. 30 of individuals, detection of gas-phase analytes finds uses in Multiple factors contribute to this heightened concern, such industrial and commercial settings. For example, some as national security issues related to the use of deadly industrial applications include monitoring product perfor chemicals as weapons, the risk of an intentional or acciden mance Such as interrogating vehicle emissions for release of tal chemical spill, environmental awareness, and increased Volatile gases. Additional applications include assessing understanding of the potential impacts of Such chemicals on 35 fruit ripeness and/or spoilage based on volatile gas emis human health. The range of applications for sensors that can sions. accurately measure volatile gases is wide. There is also broad potential for use of sensors of gas For example, the Department of Homeland Security needs phase analytes in biomedical applications. For example, sensors to detect the presence of chemical weapons, such as sensors have been used to monitor the composition of gas chemical warfare agents and explosives. These sensors can 40 mixtures used for anesthesia during Surgical procedures or to be integrated into traffic lights in large cities, as components monitor exhaled gases related to metabolic activities. of air-intake valves in municipal buildings, and used as Recently, analysis of human breath has emerged as a non on-board devices for unmanned aerial vehicles or robotic invasive technique for diagnosis of disease. The exhaled vehicles that are used to explore hazardous situations. Simi human breath contains a number of Volatile gases Such as lar sensors can be used to detect natural gas leaks for home 45 oxygen, carbon dioxide, nitrogen, carbon monoxide, and business owners and to monitor outdoor air in local acetone, ammonia, hydrogen Sulfide, amines, oxides of communities, school playgrounds, or agricultural settings. nitrogen, etc. (Manolis, 1983; Smith et al., 1999; and Diskin Approximately 70,000 illnesses and deaths occur annu et al., 2003) and measurements of analytes in exhaled breath ally as a result of occupational exposure to toxic gases, at a have been applied to a wide range of disease states, includ cost of more than S100 billion from lost wages and medical 50 ing diabetes (Henderson et al., 1952; Sulway et al., 1970; expenses. Millions of US workers in various industries are Crofford et al., 1977; and Novak et al., 2007), gastrointestinal exposed to vapors from various organic chemicals that are disorders (Perman, 1991; Bauer et al., 2000; and Nieminen et recognized by the National Institute of Occupational Safety al, 2000), and asthma (Alving et al., 1993). and Hygiene (NIOSH) as carcinogens, reproductive hazards, While current technologies exist to measure gaseous and/or neurotoxins. As such, industrial manufacturers need 55 analytes (e.g., volatile organic compounds and other com sensors to monitor facility air during production, Survey pounds), these technologies do not provide timely informa product off-gassing, and assist with maintaining safe levels tion regarding gas levels to inform immediate actions for of permissible exposure limits (PELs) to protect workers minimizing risks, e.g., taking appropriate measures in the against the health effects of exposure to hazardous Sub medical, defense, and industrial settings to protect human stances including toxic industrial chemicals. NIOSH and 60 health. For example, many direct-read dosimeters lack sen other governmental agencies such as the Environmental sitivity and reproducibility and do not meet regulatory Protection Agency, Occupational Safety and Health Agency, monitoring requirements. Alternatively, many indirect read Housing and Urban Development, and the Federal Emer technologies are shipped to an accredited laboratory for gency Management Agency are tasked with reducing the analysis, introducing a long lag-time of typically many risk, and therefore the healthcare burden, of exposure to 65 weeks between sample collection and data retrieval. In toxic gases, while attempting to minimize the impact on addition, conventional technologies are also subject to Sub industry operations and revenues. stantial positive or negative interference from other pollut US 9,575,037 B2 3 4 ants and inaccuracies resulting from low air flow. There Some embodiments, the first and second Surfaces form a exists, therefore, an unmet need for technology that accu compartment having first and second open ends, wherein the rately measures gases and that can be read on-site to provide headspace at the first end is from 1 to 20 microns and the actionable information. headspace at the second end is from 21 to 100 microns. In some situations described above, it is necessary to The thickness of the liquid crystal film is related to the know the concentration of the chemical environment as response of the device to the analyte, e.g., by controlling the quickly as possible in order to minimize exposure to the rate at which the analyte reaches a functionalized surface chemical. In Such situations a detector of the instantaneous upon which the liquid crystal has been deposited. Embodi concentration of the gas is needed. In other situations, such ments are provided in which micro-pillar features on a as but not limit to when measuring personal exposure to a 10 surface control the thickness of the liquid crystal film. vapor, it is necessary to know the cumulative exposure to the Accordingly, in some embodiments the first Surface further chemical that occurs of a given interval of time, Such as but not limited to a workday. In this situation, a dosimeter that comprises micro-pillars. The Surfaces are not limited in the measures the cumulative level of exposure over a set period materials from which they are made. For instance, some of time is needed. 15 embodiments provide that the first surface and/or the second Surface comprises a Substrate of glass, silicon, or gold. In SUMMARY Some embodiments, the second Surface is functionalized with an intert Substance. In some embodiments, the second Provided herein is technology related to sensors and surface is functionalized with (Tridecafluoro-1,1,2,2-tetra analyte detection associated with the use of liquid crystal hydrooctyl)-trichlorosilane. (LC) materials. In some embodiments, the technology Some embodiments provide a device in which the analyte relates to detecting volatile organic compounds and particu interacts directly with the liquid crystal to effect a phase in larly, but not exclusively, to methods and compositions for the liquid crystal. Some embodiments provide a device in detecting Volatile organic compounds by measuring changes which the liquid crystal contacts a Surface (e.g., a function in the physical properties of liquid crystals. In some embodi 25 alized surface) and the interaction of the analyte with the ments, the LC materials that find use in the technology functionalized surface effects an orientation of the liquid comprise rod-shaped organic molecules that form con crystal. In some embodiments, the functionalized surface densed phases. These materials possess long-range orienta comprises a functional group that is 4-aminothiophenol. In tional ordering (and are thus in Some aspects crystal-like) Some embodiments, the functionalized Surface comprises a but lack positional ordering (and are thus in Some aspects 30 liquid-like). The long-range ordering of molecules within functional group that is lead perchlorate. the LC gives rise to anisotropic optical properties and optical The technology is not limited in the liquid crystal that is birefringence. The interaction of gas-phase analytes with used to indicate the presence of the analyte. For example, particular LC materials and or with the Surface Supporting it Some exemplary liquid crystals that find use in the technol modifies the long-range order or orientation of the LCs and 35 ogy are MBBA, MLC-2080, MLC-2081, and E7, and mix produces distinct changes in the optical appearance of the tures thereof. Various liquid crystal compositions find use in LC, thus providing a measurable indicator associated with embodiments of the technology. For instance, in some the analyte. embodiments the liquid crystal composition comprises a Accordingly, Some embodiments of the technology pro cyanobiphenyl compound. vide methods for detecting an analyte (e.g., a VOC) in a 40 Particular exemplary embodiments of the technology gaseous phase, the method comprising providing a liquid detect the analytes H.S., HCHO, NO, toluene, benzene, crystal assay device; exposing the liquid crystal assay device Xylene, nitrobenzene, hexane, alcohol, gasoline, and com to a sample Suspected of comprising an analyte; and inter ponents of gasoline (e.g., octane, etc.). rogating the liquid crystal assay device to detect the analyte, A phase change in a liquid crystal can be associated with wherein a change in a property of the liquid crystal com 45 a change in the optical anisotropy, magnetic anisotropy, position in the liquid crystal assay device caused by an dielectric anisotropy, and/or the presence of a phase transi interaction of the analyte with the liquid crystal assay device tion temperature. Accordingly, some embodiments provide is indicative of the presence of the analyte. In some embodi methods wherein the interrogation comprises measuring a ments the liquid crystal assay device comprises a first change in a property selected from the group consisting of Surface contacting a composition comprising a liquid crys 50 optical appearance, optical anisotropy, magnetic anisotropy, tal; a second Surface; and a headspace between the compo dielectric anisotropy, rheology, optical absorbance, and sition comprising the liquid crystal and the second Surface. phase transition temperature. In some embodiments, expos In some embodiments, the first Surface comprises a func ing the liquid crystal assay device to a sample Suspected of tional group and an interaction of the analyte with the comprising an analyte causes a phase transition in the liquid functional group causes the change in the property of the 55 crystal composition from a first phase selected from the liquid crystal composition. For example, Some embodiments group consisting of an isotropic phase, a nematic phase, or provide that the functional group is specific for the analyte. a Smectic phase to a second phase selected from the group In some embodiments, detection of the analyte is cumula consisting of an isotropic phase, a nematic phase, and a tive. In some embodiments, the change in a property of the Smectic phase. In some embodiments, the liquid crystal liquid crystal composition is detectable in real-time. In some 60 composition undergoes an orientational transition in the embodiments, the presence of said analyte is detected in presence of the analyte. Such as a change in the orientation real-time. The headspace is related to the rate of exposure of of the optical axis of the liquid crystal (e.g., a change in the the device to the analyte and, as Such, provides a function tilt of the liquid crystal from the surface normal). In some ality to control the rate of exposure of the device to the exemplary embodiments, the orientational transition is analyte. In some embodiments, the headspace is 1 to 100 65 selected from the group consisting of a homeotropic align microns, 5 to 50 microns, or, in some embodiments, 10 to 25 ment changing to a planar alignment, a random planar microns. In some embodiments, the headspace is variable. In alignment changing to a uniform planar alignment, a uni US 9,575,037 B2 5 6 form planar alignment changing to a random planar align liquid crystal assay device to a sample Suspected of com ment, and a planar alignment changing to a homeotropic prising an analyte causes a phase transition in the liquid alignment. crystal composition from a first phase selected from the Embodiments are provided in which a headspace provides group consisting of an isotropic phase, a nematic phase, a a channel for access of the analyte to the device and liquid 5 liquid crystal phase rich in chiral dopants, a frustrated phase, crystal. As such, some embodiments provide that the second a blue phase, a ferroelectric phase, a twisted grain boundary Surface does not contact the composition comprising the phase, or a Smectic phase to a second phase selected from the liquid crystal. group consisting of an isotropic phase, a nematic phase, and In some embodiments, the concentration or accumulated a Smectic phase, a liquid crystal phase rich in chiral dopants, exposure to an analyte is related to the size of an area of the 10 a frustrated phase, a blue phase, a ferroelectric phase, a device in which the liquid crystal has undergone a phase twisted grain boundary phase. In some embodiments, the change (a "reacted area of the device). Consequently, liquid crystal composition undergoes an orientational tran embodiments are provided in which method comprise quan sition in the presence of the analyte, wherein the orienta tifying an analyte concentration by measuring a size of a LC tional is a change in the orientation of the optical axis of the responded area. For instance, in Some embodiments the 15 liquid crystal. In some exemplary embodiments, the orien methods comprise quantifying an analyte concentration by tational change is selected from the group consisting of a measuring a distance of a birefringent front from a site of homeotropic alignment changing to a planar alignment, a exposure of the liquid crystal assay device to the sample random planar alignment changing to a uniform planar Suspected of comprising the analyte. In some embodiments, alignment, a uniform planar alignment changing to a random measuring an anisotropy provides an observable property to planar alignment, and a planar alignment changing to a differentiate the phases (e.g., the “unreacted area” and the homeotropic alignment. In other embodiments, the orienta “reacted area') and thus assess the size (e.g., the length) of tional transition involves a change in the tilt of the liquid the reacted area. In some embodiments, the anisotropy is an crystal away from the Surface normal. optical anisotropy and the interrogation comprises measur In some embodiments, the concentration or accumulated ing a reflection or a transmission of polarized light. In some 25 exposure to an analyte is related to the size of an area of the embodiments, measurement of the rate of increase in the device in which the liquid crystal has undergone a phase or reacted area is used to indicate the concentration of the orientational change (a "reacted area of the device). Con analyte present around the device. sequently, embodiments are provided in which method com In some embodiments, methods are provided detecting an prise quantifying an analyte concentration by measuring a analyte in a gaseous phase, the methods comprising provid 30 size of a reacted area. For instance, in some embodiments ing a liquid crystal assay device comprising a Surface in a the methods comprise quantifying an analyte concentration channel; exposing the liquid crystal assay device to a sample by measuring a distance of a birefringent front from a site of Suspected of comprising an analyte; contacting the Surface exposure of the liquid crystal assay device to the sample with a liquid crystal; and interrogating the liquid crystal Suspected of comprising the analyte. In some embodiments, assay device to detect the analyte, wherein a change in a 35 measuring an anisotropy provides an observable property to property of the liquid crystal composition in the liquid differentiate the phases (e.g., the “unreacted area” and the crystal assay device caused by an interaction of the analyte “reacted area') and thus assess the size (e.g., the length) of with the liquid crystal assay device is indicative of the the reacted area. In some embodiments, the anisotropy is an presence of the analyte. In these embodiments, the Surface is optical anisotropy and the interrogation comprises measur reacted with the analyte and the liquid crystal is applied to 40 ing a reflection or a transmission of polarized light. “read the reacted portion of the surface. For instance, in In some embodiments, the size of the reacted area is on Some embodiments the Surface comprises a functional group the order of 1, 10, 100, or 1000 mm. For example, in some and an interaction of the analyte with the functional group embodiments the distance measured for a reacted area is causes the change in the property of the liquid crystal from about 1 micron about 200 mm, for example, from about composition. Particular embodiments provide that the func 45 1 micron to 1 mm, 1 micron to 10 mm, 1 micron to 50 mm, tional group is specific for the analyte. 1 micron to 100 mm, 1 micron to 200 mm, 1 mm to 10 mm, The surfaces are not limited in the materials from which 1 mm to 50 mm, 1 mm to 100 mm, 1 mm to 200 mm, 10 mm they are made. For instance. Some embodiments provide that to 100 mm or 10 mm to 200 mm. the first Surface and/or the second Surface comprises a The technology finds use in monitoring exposure (e.g., of Substrate of glass, silicon, or gold. 50 a person) to a gaseous analyte Such as a toxic gas. Accord Some embodiments provide a device in which the liquid ingly, embodiments of methods are provided for monitoring crystal contacts a surface (e.g., a functionalized surface) and a Subject’s exposure to a toxic gas, the methods comprising the interaction of the analyte with the functionalized surface providing to the Subject a dosimeter badge comprising a effects a phase change in the liquid crystal. In some embodi liquid crystal assay device; measuring a change in a property ments, the functionalized surface comprises a functional 55 of a liquid crystal composition in the liquid crystal assay group that is 4-aminothiophenol. In some embodiments, the device caused by an interaction of the toxic gas with the functionalized Surface comprises a functional group that is liquid crystal composition; and reporting an exposure to the lead perchlorate. toxic gas. Monitoring methods comprise use of embodi A phase change in a liquid crystal causes a change in a ments of devices provided herein. In some embodiments the composition comprising the liquid crystal Such as a change 60 devices report exposure in real-time to provide an immediate in the optical anisotropy, magnetic anisotropy, dielectric signal of exposure. In some embodiments, the devices report anisotropy, and/or phase transition temperature. Accord a cumulative exposure over an amount of time (e.g., 1 to 100 ingly, some embodiments provide methods wherein the minutes; 1 to 10 days; 1 to 10 weeks; or more). In some interrogation comprises measuring a change in a property embodiments, detection of the analyte is in real-time. selected from the group consisting of optical anisotropy, 65 Embodiments comprise methods relate to a liquid crystal magnetic anisotropy, dielectric anisotropy, and phase tran assay device that comprises a first Surface contacting a sition temperature. In some embodiments, exposing the composition comprising a liquid crystal; a second Surface; US 9,575,037 B2 7 8 and a headspace between the composition comprising the polymer is a polystyrene, a polyvinyl acetate, or a fluoro liquid crystal and the second surface. Further embodiments alcohol polycarbosilane. Furthermore, in some embodi are provided wherein the liquid crystal assay device com ments the polymer is mechanically rubbed. prises a Surface in a channel and the method further com In some embodiments the surface is a hydrocarbon film prises contacting the Surface with a liquid crystal. deposited on a Substrate. For example, Some embodiments In some embodiments, the devices are distinguishable provide that the hydrocarbon film comprises a long chain from other dosimeter devices, such as electrochemical aliphatic hydrocarbon, for instance in Some embodiments a devices, based on the mass of the device. In some preferred hydrocarbon film that is solid at room temperature and is embodiments, the devices of the present invention have a soluble in the Volatile organic compound or is plasticized by mass of from about 5 to 50 grams, preferably from about 10 10 the Volatile organic compound. In some embodiments the to 30 grams or from 10 to 20 grams. hydrocarbon comprises an aliphatic chain of 18 or more In some embodiments, the present invention provides a carbons. sensor device comprising a first Substrate having a surface The methods detect volatile organic compounds over a modified with an amine moiety, said Surface having disposed range of concentrations. Exemplary embodiments are pro thereon a liquid crystal composition that is homeotropically 15 vided wherein the method detects a volatile organic com aligned in the presence of the amine moiety. In some pound of at least approximately 50 ppm. embodiments, the Substrate comprises a gold film disposed In some embodiments, the liquid crystal composition is on an underlying base Substrate. In some embodiments, the utilized in the form of polymer dispersed liquid crystal and substrate further comprises an intervening layer between the in some particular embodiments the polymer dispersed base Substrate and said gold film. In some embodiments, the liquid crystal is formed in the liquid crystal assay device in intervening layer is a metallic adhesion layer selected from a strained configuration. the group consisting of titanium and chromium. In some In some embodiments, the Surface comprises a cavity and embodiments, the amine moiety is 4-aminothiophenol. In the liquid crystal composition is confined in the cavity. Some embodiments, the Substrate is a glass Substrate. In In some embodiments the liquid crystal composition is Some embodiments, the amine moiety is p-aminophenylt 25 confined in a polymer matrix. In some embodiments, the rimethoxysilane. In some embodiments, the liquid crystal liquid crystal composition is a polymer dispersed liquid composition comprises MBBA. In some embodiments, the crystal deposited on a rubbed polymer film. In some embodi sensor devices further comprise a second Substrate oriented ments, the polymer dispersed liquid crystal comprises drop opposite of the first Substrate to define a compartment. In lets having a diameter of less than 2 microns. Some embodiments, the compartment has a headspace 30 In some embodiments, the Surface comprises an ionic salt. between the liquid crystal composition disposed on said first For example, in Some embodiments the Surface comprises a substrate and said second substrate. In some embodiments, first ionic salt that is soluble in the volatile organic com the headspace is 1 to 100 microns. In some embodiments, pound and a second ionic salt that is not soluble in the the headspace is 5 to 50 microns. In some embodiments, the Volatile organic compound. Exemplary ionic salts include a headspace is 10 to 25 microns. In some embodiments, the 35 quaternary ammonium, a tetraphenylborate, or a metal per headspace is variable. In some embodiments, the first and chlorate salt. second Surfaces form a compartment having first and second In some embodiments, the liquid crystal comprises a open ends, wherein the headspace at the first end is from 1 polymer bead. to 20 microns and the headspace at the second end is from Volatile organic compounds induce changes in a variety of 21 to 100 microns. 40 physical characteristics of the liquid crystal compositions. In some embodiments, the technology provides a method For example, in Some embodiments exposing the liquid for detecting a volatile organic compound in a gaseous crystal assay device to a sample Suspected of comprising a phase, the method comprising providing a liquid crystal Volatile organic compound causes a phase transition in the assay device comprising a Surface in contact with a liquid liquid crystal composition. In some embodiments exposing crystal composition; exposing the liquid crystal assay device 45 the liquid crystal assay device to a sample Suspected of to a sample Suspected of comprising a volatile organic comprising a volatile organic compound causes a structural compound; and interrogating the liquid crystal assay device change of the liquid crystal composition confined in a to detect the volatile organic compound, wherein a change in microstructure. In some embodiments exposing the liquid a property of the liquid crystal composition in the liquid crystal assay device to a sample Suspected of comprising a crystal assay device caused by an interaction of the volatile 50 Volatile organic compound causes a dewetting of a polymer organic compound with the liquid crystal assay device is film on the Substrate. In some embodiments exposing the indicative of the presence of the volatile organic compound. liquid crystal assay device to a sample Suspected of com In some embodiments, the Surface comprises a Substrate of prising a volatile organic compound causes a structural glass, gold, or silicon and in some embodiments the Surface change in a polymer film Supporting the liquid crystal comprises micro-pillars. 55 composition. In some embodiments exposing the liquid Various liquid crystal compositions find use in embodi crystal assay device to a sample Suspected of comprising a ments of the technology. For instance, in Some embodiments Volatile organic compound causes dissolution of an ionic salt the liquid crystal composition comprises a cyanobiphenyl into the liquid crystal composition. In some embodiments compound. Furthermore, the technology is directed toward exposing the liquid crystal assay device to a sample Sus detecting various volatile organic compounds, e.g., in some 60 pected of comprising a volatile organic compound causes embodiments the Volatile organic compound is toluene, Swelling of a polymer bead Suspended in the liquid crystal benzene, Xylene, nitrobenzene, hexane, or an alcohol. In composition. other embodiments, the Volatile organic compound is Changes in physical characteristics of the liquid crystal octane, gasoline, painer thinner or Stove alcohol. composition are monitored or interrogated by various meth In some embodiments, the Surface is a polymer deposited 65 ods. In some embodiments the interrogation comprises on a Substrate. The technology is not limited in the polymer measuring a change in a property Such as optical anisotropy, that is deposited. For example, in Some embodiments the magnetic anisotropy, rheology, optical absorbance, dielectric US 9,575,037 B2 10 anisotropy, or phase transition temperature. In some embodi FIG. 6 shows images of sandwich cells after exposure to ments the change in the property of the liquid crystal 8 ppm HS/45% relative humidity for eight hours (FIG. 6A) composition in the liquid crystal assay device caused by and to Zero air control at 45% relative humidity for eight interaction of the Volatile organic compound with the liquid hours (FIG. 6B). crystal assay device is a change in transmission of polarized 5 FIG. 7 shows images of microfluidic cells after exposure light. to 8 ppm HS/45% relative humidity for eight hours (FIG. In some embodiments the liquid crystal assay device 7A) and to zero air control at 45% relative humidity for eight comprises an array of discrete assay areas and an internal hours (FIG. 7B). calibration area and wherein the interrogation comprises FIG. 8 is a series of images acquired of cumulative 10 analyte sensors. FIG. 8A shows a sensor exposed to HS for comparing the response of an assay area to the internal 0 ppm-hour. FIG. 8B shows a sensor exposed to HS for 0.8 calibration area. ppm-hour. FIG. 8C shows a sensor exposed to HS for 4 In some embodiments the Surface has a form selected ppm-hour. FIG. 8D shows a sensor exposed to HS for 8 from the group consisting of planar, spherical, and cylindri ppm-hour. FIG. 8E shows a sensor exposed to HS for 25 cal. In some embodiments the Surface is a patterned surface, 15 ppm-hour. FIG. 8F shows a sensor exposed to HS for 40 for example, a patterned Surface that comprises a feature ppm-hour. FIG. 8G shows a sensor exposed to HS for 80 Such as a grid, a channel, a pillar, or an assay area, or a ppm-hour. FIG. 8H shows a sensor exposed to HS for 120 combination thereof. In some embodiments, the features are ppm-hour. FIG. 8I shows a sensor exposed to HS for 160 1 to 50 microns high, 1 to 200 microns wide, and spaced 1 ppm-hour. FIG. 8J shows a sensor exposed to HS for 16 to 200 micron apart. Moreover, in some embodiments the ppm-hour verify quality control. pillars have a form that is circular, triangular, Square, or FIG. 9 is a plot showing the length of the response front hexagonal. versus HS exposure dose for an HS sensor. In some embodiments, exposing the liquid crystal assay FIG. 10 is a plot showing the length of the response front device to a sample Suspected of comprising a volatile versus the square root of the HS exposure dose for an H.S organic compound causes a phase transition in the liquid 25 SSO. crystal composition from a first phase that is an isotropic FIG. 11 shows the effect of thickness of the headspace phase, a nematic phase, or a Smectic phase to a second phase height on the response of microfluidic sensor. that is an isotropic phase, a nematic phase, and a Smectic FIG. 12 shows the effect of different concentrations of phase. In some embodiments the liquid crystal composition HS on response from microfluidic sensor. undergoes an orientational transition in the presence of the 30 FIG. 13 shows the response from a microfluidic sensor volatile organic compound, wherein the orientational tran with 45 micron head space and with micropillared area sition is a homeotropic alignment changing to a planar extending to the edge. alignment, a random planar alignment changing to a uniform FIG. 14 shows variation of the response length as a planar alignment, a uniform planar alignment changing to a function of the exposure time for real-time detection of HS 35 using microfluidic cell. random planar alignment, or a planar alignment changing to FIG. 15 shows the optical response of a liquid crystal a homeotropic alignment. In some embodiments, the liquid sensor exposed to 17.5 ppm HCHO and non-targeted vapors. crystal undergoes an orientational transition that changes the The transmitted light intensity was captured by digital tilt of the liquid crystal from the normal. In some embodi camera and expressed as brightness. ments the liquid crystal composition comprises a dopant. 40 FIG. 16 shows the detection of cumulative exposure to Additional embodiments will be apparent to persons HCHO using liquid crystal-based dosimeter badges. FIG. skilled in the relevant art based on the teachings contained 16a shows a depiction of formaldehyde vapor diffusing into herein. the headspace and into the LC film, thus generating a lateral concentration gradient that is seen as a dark front on each BRIEF DESCRIPTION OF THE DRAWINGS 45 side of the badge (FIG. 16b). FIG.16c is a plot showing the measured light intensity decreasing linearly with exposure These and other features, aspects, and advantages of the time. present technology will become better understood with FIG. 17 shows Fourier transform infrared spectra regard to the following drawings: acquired of a Surface comprising an 4-aminothiophenol film FIG. 1 shows images of 2x5 sensors before exposure to 50 before (spectrum A) and after (spectrum B) exposure to HS (FIG. 1A), long sensors #1 to #4 before exposure to HS NO. (FIG. 1B), and sandwich cells comprising mylar of 25 FIG. 18 shows a Fourier transform infrared spectrum microns and 50 microns before exposure to HS (FIG. 1C). acquired of a 100 A silicon wafer comprising a 4-aminoth The bright stripe at the middle of the FIG. 1A right side is iophenol film. duel to the mylar strip. 55 FIG. 19 shows Fourier transform infrared spectra FIG. 2 shows images of 2x5 sensors after exposure to 1 acquired of a 100 A gold surface comprising an 4-amino ppm HS (FIG. 2A), long sensors #1 to #4 after exposure to thiophenol film before (spectrum A) and after (spectrum B) 1 ppm HS (FIG. 2B), and sandwich cells comprising mylar exposure to NO. of 25 microns and 50 microns after exposure to 1 ppm HS FIG. 20 shows the alignment of different liquid crystals on (FIG. 2C). 60 surfaces functionalized with 4-aminothiophenol before FIG. 3 shows an image of the long sensor #3 from FIGS. (FIG. 20A) and after exposure to NO, (FIG. 20B). 1 and 2 after storage at ambient conditions for several days FIG. 21 shows the selective detection of NO relative to after exposure. humid gas. FIG. 4 shows sandwich cells prior to exposure to analyte FIG. 22 shows Fourier transform infrared spectra (FIG. 4A) or a zero air control (FIG. 4B). 65 acquired of a surface comprising a 4-aminothiophenol film FIG. 5 shows images of microfluidic cells prior to expo before (grey) and after (black) exposure to N (top spectra) sure to analyte (FIG. 5A) or a zero air control (FIG. 5B). and NO (bottom spectra). US 9,575,037 B2 11 12 FIG. 23 shows the detection of NO using channels that absorbs VOCs. Upon exposure to VOCs, the polymer defined by a polydimethylsiloxane channel. The images structure changes to an anisotropic shape due to the con were acquired 2 minutes after filling the LC cell strained boundary conditions. (b) As a result, the LC under FIG. 24 shows an embodiment of a sensing device com goes change in orientation inside the modified structure. prising a polydimethylsiloxane channel used to define the FIG. 35 is a schematic showing a basic principle of exposure path on a functionalized surface to increase the detection of VOCs using dewetting-induced orientational sensitivity of detection. transition of LCs. A glass Substrate is coated with polymer FIG. 25 shows the detection of different concentrations of (PS) and a film of LC is supported on the polymer film. NO using polydimethylsiloxane channels to define the When the film is exposed to VOCs, the film dewets the exposure path. 10 Surface and the orientation of LC changes. FIG. 26 shows a series of optical images demonstrating FIG. 36 is a schematic showing a basic principle of the response of an embodiment of the technology to different detection of VOCs based on structural changes on the concentrations of NO (FIG. 26A). FIG. 26B shows a linear Surface Supporting a LC film. A polymer film that is known relationship between the length of the bright channel and the to absorb target analyte is deposited and mechanically NO concentration. 15 sheared to generate micro-structures on the Surface. These FIG. 27 shows the alignment of three liquid crystals microstructures align LC in a pre-defined direction. Absorp having a negative dielectric anisotropy. FIG. 27A, FIG. 27B, tion of VOCs into the polymer film erases the microstruc and FIG. 27C shows the alignment of the liquid crystals tures inducing a change in orientation of LCs film. MBBA, MLC-2080, and MLC-2081, respectively. FIGS. 37A, 37B, and 37C are a schematic showing a basic FIG. 28 shows the alignment of mixtures of MBBA and principle of detection of VOCs using orientation transition MLC-2080 at different ratios of MBBA to MLC-2080. induced by dissolution of ionic salt into LC film. A thin film Panels (a) through (h) show the alignment of MLC-2080 of ionic salt is deposited on self-assembled monolayer alone; mixtures of MLC-2080 and MBBA at ratios of 0.9 formed on a gold coated surface. When the LC film is MLC-2080, 0.8 MLC-2080, 0.7 MLC-2080, 0.6 MLC-2080, exposed to target VOC, the ionic salt radially dissolves into 0.5 MLC-2080, and 0.25 MLC-2080; and MBBA alone, 25 the LC film thereby inducing orientational transition in the respectively. LC film. FIG. 29 shows on optical image of a liquid crystal cell FIG. 38 is a schematic showing a basic principle of fabricated with a 4-aminothiophenol functionalized surface detection of VOCs using orientation transition induced by exposed to NO, for different times and filled with liquid localized concentration at defect sites in LC. A thin film of crystal compositions. Panels (a) through (c) are images of a 30 LC is Supported on a rough surface that generates local cell exposed to 20 ppb humid NO for 10 minutes then filled defects in the LC at the microscopic level, yet providing with MBBA, a cell exposed to 20 ppb humid NO, for 5 uniform alignment on macroscopic level. When the surface minutes then filled with MBBA, and a cell exposed to 20 ppb is exposed to VOCs, the microscopic defects locally con humid NO for 5 minutes then filled with a mixture of centrate the VOC molecules at the defect sites leading to MLC-2080 and MBBA at a 60 to 40 ratio. 35 ordering transition in the LC film FIG. 30 shows optical images of cells comprising 4-ami FIG. 39 is a schematic showing a basic principle of nothiophenol functionalized surfaces. Panels (a) through (f) detection of VOCs utilizing swelling of polymer beads show cells exposed to 20 ppb humid NO at 800 sccm for 2 suspended in LC. Polymer beads are suspended in a LC film minutes and filled with pure MBBA: 10 ppb humid NO at that is supported on a surface providing uniform alignment 800 scom for 2 minutes and filled with MLC-2080 and 40 of LC. Absorption of VOC in the polymer beads swells the MBBA at a 60 to 40 ratio; (c) 10 ppb humid NO at 400 sccm beads and induces distortion in the LC alignment around the for 2 minutes and filled with MLC-2080 and MBBA at a 60 beads. The distorted LC around these beads scatters light. to 40 ratio; (d) humid N at 400 sccm for 2 minutes and filled FIG. 40 is a schematic showing an experimental system with MLC-2080 and MBBA at a 60 to 40 ratio; (e) 20 ppb for exposing sensors to VOC. humid NO at 800 sccm for 30 seconds and filled with 45 FIG. 41 is a plot showing the response of a LC sensor MLC-2080 and MBBA at a 60 to 40 ratio; and (f) image of exposed to 5000 ppm toluene. The light intensity transmitted (e) after overnight storage at room temperature. through the sensor between crossed polarizers (mean gray FIG. 31 shows images of a LC cell comprising a 4-ami scale intensity-MGSI) was measured as a function of expo nothiophenol treated gold surface exposed to different con Sure time. The inset shows the visual appearance of the centrations of NO and filled with a liquid crystal (MLC 50 sensor between crossed polarizers before (bright) and after 2080 and MBBA at a 65 to 35 ratio). Concentrations of NO, (dark) the vapor exposure. The sensor reverted back to initial tested were from 10 to 40 ppb in 5 ppb increments and 40 appearance immediately after the toluene Supply was to 100 ppb in 10 ppb increments. ceased. FIG. 32 shows a plot of data collected from analyzing the FIG. 42 shows optical images of LC cells prepared with series of images shown in FIG. 31. 55 polystyrene (PS) and low molecular weight PS (low MW FIG. 33 is schematic showing a principle of detection of PS) polymer coated on a glass Surface by pairing with organic vapors using liquid crystals (LCs) using phase Tridecafluoro-1,1,2,2-tetrahydrooctylkrichlorosilane (OTS) transition. The initial and post exposure appearance of the coated Substrates. The polymer coated Substrates were un LC sensor depends on the surface the LC is laid onto. (A) A rubbed (a and c) and rubbed (b and d). These images were sensor consists of a thin film of LC Supported on a Substrate 60 taken with the LC cells between crossed polarizers (A: with polymeric micropillars and (B) initially appears bright analyzer and P: polarizer) with the rubbing direction ori (left). When the sensor is exposed to analyte (e.g., toluene), ented at 0° (left) and 45° (right) with respect to the crossed the LC material turns into an isotropic material and appears polarizers dark (right) between crossed polarizers. In FIG. 43, FIG. 43A shows optical images of LC FIG. 34 is a schematic showing a principle of detection of 65 sandwich cells prepared with rubbed polystyrene (PS) and VOCs using confined LCs. (a) ALC droplet is encapsulated OTS coated substrates “before’ (left) and “after (right) 20 in a micro?nano structure formed in a polymeric material hours of toluene exposure. The sandwich cells were exposed US 9,575,037 B2 13 14 to 8605 ppm (top), 5020 ppm (middle), and 0 ppm (bottom) toluene. (d) The optical response of PDLC sensors to 8600 toluene, respectively. Optical images were taken with the ppm toluene in comparison to pure E7 sensors. rubbing direction at 0° (left) and 45° (right) with respect to FIGS. 53A, 53B, and 53C are images showing the mor the crossed polarizers. FIG. 43B shows the raw images of phology of PDLC droplets. FIG. 53A shows PDLC droplets LC sandwich cells that were collected at different time 5 before incubation at 50° C. for 2 minutes. FIG. 53B shows intervals while exposed to 8605 ppm (top), 5020 ppm PDLC droplets after incubation at 50° C. for 2 minutes and (middle), and 0 ppm (bottom) toluene, respectively. FIG. FIG. 53C shows PDLC droplets after exposure to 8600 ppm 43C shows the light intensity transmitted through the LC toluene. The images were taken with a polarizing micro sandwich cells between crossed polarizers (mean gray scale scope with 50x magnification objective. intensity-MGSI) measured as a function of exposure time. 10 FIG. 54 is a plot showing optical response from PDLC FIG. 44 shows optical images of LC cells prepared with sensors at different concentrations of toluene diluted in dry poly(vinyl)acetate (PVAc) and OTS coated substrates. The nitrogen. One sensor was exposed to nitrogen for long time. PVAc coated substrates were (a) un-rubbed & unexposed, One sensor used exposed to 4000 PPM toluene was exposed (b) un-rubbed & exposed, (c) rubbed & unexposed, and (d) to 8000 PPM toluene after 5 minutes. Similarly, one sensor rubbed & exposed. 28,680 ppm toluene was used for expo 15 exposed to 8000 PPM toluene was exposed to dry nitrogen sure prior to cell fabrication. Optical images were taken with after 5 minutes. rubbing direction at 0° and 45° with respect to crossed FIG. 55 is a plot showing optical response from PDLC polarizers. sensor upon sequential exposure to 4000 ppm toluene and FIG. 45 shows optical images of LC cells prepared with dry N. rubbed PVAc and OTS coated Substrates. The PVAc coated FIG. 56 is a schematic and series of images showing substrates were rubbed five times or only once and exposed change in the PDLC droplets supported on rubbed polymer to toluene prior to cell fabrication. (a) rubbed (5 times) & film. The images show the appearance of PDLC droplets exposed (8605 ppm), (b) rubbed (1 time) & exposed (0 formed on rubbed surfaces before and after exposure to ppm), (c) rubbed (1 time) & exposed (8605 ppm), (d) rubbed toluene at different concentrations. All these exposure (1 time) & exposed (5020 ppm), and (e) rubbed (1 time) & 25 experiments were performed at 45% relative humidity. exposed (2868 ppm). Optical images were taken with rub FIG. 57 is a series of images showing the macroscopic bing direction at 0° and 45° with respect to crossed polar appearance of PDLC droplets (a) before exposure, (b) after 1Z.S. exposure to 8000 ppm toluene for 8 minutes, (c) same sensor FIG. 46 shows images of LC(E7) alignment of the chip rotated by 45°, and (d) rotated chip exposed to 8000 exposed and unexposed optical cells prepared using rubbed 30 ppm toluene after 8 minutes. All these exposure experiments or unrubbed SC-F103 polymer (Seacoast Science Inc.) were performed at 45% relative humidity. coated substrates. For rubbed polymer surfaces rubbing was FIG. 58 is a plot showing the optical response from PDLC done with a piece of velvet cloth rubbed one way for five droplets formed on rubbed surface to toluene at different times before LC addition. A) Images of unexposed sandwich concentrations. cells made with different types of SC-F103 surfaces on 35 FIG. 59 is a series of images showing the alignment of LC glass, a) uncoated; b) unrubbed SC-F103; c) rubbed on untreated glass Surfaces and Surfaces coated with PS SC-F103; d) images of the rubbed SC-F103 cell taken with paired with different top surfaces. The images were taken rubbing direction at 0° and 45° with respect to crossed with polarizing optical microscopic with 4.x and 50x mag polarizers. B) Images of a cell prepared with unrubbed nifications (as shown) and a camera before and after anneal SC-F103 coated surface before and after exposure to 5020 40 ing the LC cells for 10 minutes inside an oven at 70° C. The ppm toluene for 26 hours. Similar images were collected insets on the second column show conoscopic images. using the cells made with rubbed SC-F103 coated surface FIG. 60 comprises images showing the microscopic (4x) before and after 23 hours of exposure to C) 5020 ppm change in appearance of a LC cell upon thermal treatment. toluene and D) dry nitrogen, respectively. The formation of the microscopic domains resemble a FIG. 47 shows long chain hydrocarbons tested in experi 45 typical pattern observed in dewetting of polymer films. ments described herein. FIG. 61 provides images showing the appearance of a FIG. 48 shows in (A) a schematic for making a thin sensor upon exposure to saturated vapor of toluene. hydrocarbon film on a 3"x 1" glass slide and in (B) the FIG. 62 is a series of images showing the macroscopic images of 1" x 1" glass slides with LC (E7) coated on top of appearance of sensor upon exposure to 5000 ppm toluene (at a hydrocarbon (C18) layer between crossed polarizers. 50 50% RH) for different durations. The last two images show FIG. 49 shows (A) images of an LC sensor collected the microscopic appearance after overnight exposure to while exposed to 5020 ppm toluene vapor. (B) Images of the 5000 ppm toluene (50% RH) at 4x and 50x magnification, same sensor collected off line before and after 19 hours of respectively. toluene exposure. FIG. 63 shows the macroscopic (camera) and microscopic FIG. 50 shows images of A) a portion of the sandwich 55 appearance of sensor fabricated on micropillared Substrate. cells containing (i) octadecane and E7 and (ii) octadecane The polarizing optical microscopic (POM) image on the left alone from 5 hours of 5020 ppm toluene exposure. B) 5020 shows the bright lines due to planar alignment of LC. ppm toluene exposure to the E7 and E7-octadecane mixture FIG. 64 shows the appearance of micro-pillared sensor spotted on a glass piece. before and after exposure to nitrogen (a: before exposure) FIG. 51 shows images from experiments testing 5020 60 and (b: after 30 minutes exposure) and 2000 ppm toluene (c: ppm toluene exposure to a sandwich cell prepared by pairing before exposure), (d: 30 minutes exposure) and (e: after 4 a substrate coated with C24 film and an OTS coated glass hour exposure). Plot (f) shows a quantitative measurement pieces. The gap between two substrates was filled with LC of the response. E7. It is to be understood that the figures are not necessarily FIG. 52 shows the detection of toluene vapor using 65 drawn to Scale, nor are the objects in the figures necessarily PDLCs. (a) to (c) Microscopic pictures of PDLCs (a) before, drawn to scale in relationship to one another. The figures are (b) during, and (c) after exposure to a high concentration of depictions that are intended to bring clarity and understand US 9,575,037 B2 15 16 ing to various embodiments of apparatuses, systems, and many cases, the wavefront is visually detectable. However, methods disclosed herein. Wherever possible, the same the location of the wavefront can also be detected by image reference numbers will be used throughout the drawings to analysis procedures. refer to the same or like parts. Moreover, it should be As used herein, the term “ligand refers to any molecules appreciated that the drawings are not intended to limit the that bind to or can be bound by another molecule. Scope of the present teachings in any way. As used herein, the term “detection region” refers to a discreet area that is designated for detection of an analyte in DETAILED DESCRIPTION a sample. As used herein, the terms “material' and “materials' refer Provided herein is technology relating to detecting gas 10 to, in their broadest sense, any composition of matter. eous analytes and particularly, but not exclusively, to As used herein, the term “field testing refers to testing devices and methods related to detecting gaseous analytes that occurs outside of a laboratory environment. Such testing by monitoring changes in liquid crystals upon exposure to can occur indoors or outdoors at, for example, a worksite, a the gaseous analytes. place of business, public or private land, or in a vehicle. The section headings used herein are for organizational 15 As used herein, the term "nanostructure” refers to a purposes only and are not to be construed as limiting the microscopic structure, typically measured on a nanometer described Subject matter in any way. scale. Such structures include various three-dimensional In this detailed description of the various embodiments, assemblies including, but not limited to, liposomes; films; for purposes of explanation, numerous specific details are multilayers; braided, lamellar, helical, tubular, and fiber-like set forth to provide a thorough understanding of the embodi shapes; and combinations thereof. Such structures can, in ments disclosed. One skilled in the art will appreciate, Some embodiments, exist as Solvated polymers in aggregate however, that these various embodiments may be practiced forms such as rods and coils. Such structures can also be with or without these specific details. In other instances, formed from inorganic materials, such as prepared by the structures and devices are shown in block diagram form. physical deposition of a gold film onto the Surface of a solid, Furthermore, one skilled in the art can readily appreciate that 25 proteins immobilized on Surfaces that have been mechani the specific sequences in which methods are presented and cally rubbed, and polymeric materials that have been performed are illustrative and it is contemplated that the molded or imprinted with topography by using a silicon sequences can be varied and still remain within the spirit and template prepared by electron beam lithography. Scope of the various embodiments disclosed herein. As used herein, the term “self-assembling monomers' All literature and similar materials cited in this applica 30 refers to molecules that spontaneously associate to form tion, including but not limited to, patents, patent applica molecular assemblies. In one sense, this can refer to surfac tions, articles, books, treatises, and internet web pages are tant molecules that associate to form surfactant molecular expressly incorporated by reference in their entirety for any assemblies. The term “self-assembling monomers' includes purpose. Unless defined otherwise, all technical and scien single molecules and Small molecular assemblies, whereby tific terms used herein have the same meaning as is com 35 the individual small molecular assemblies can be further monly understood by one of ordinary skill in the art to which aggregated (e.g., assembled and polymerized) into larger the various embodiments described herein belongs. When molecular assemblies. definitions of terms in incorporated references appear to As used herein, the term “linker' or “spacer molecule' differ from the definitions provided in the present teachings, refers to material that links one entity to another. In one the definition provided in the present teachings shall control. 40 sense, a molecule or molecular group can be a linker that is covalent attached to two or more other molecules (e.g., DEFINITIONS linking a ligand to a self-assembling monomer). As used herein, the term “bond refers to the linkage To facilitate an understanding of the present technology, between atoms in molecules and between ions and mol a number of terms and phrases are defined below. Additional 45 ecules in crystals. The term “single bond refers to a bond definitions are set forth throughout the detailed description. with two electrons occupying the bonding orbital. Single Throughout the specification and claims, the following bonds between atoms in molecular notations are represented terms take the meanings explicitly associated herein, unless by a single line drawn between two atoms (e.g., C-C). The the context clearly dictates otherwise. The phrase “in one term “double bond refers to a bond that shares two electron embodiment as used herein does not necessarily refer to the 50 pairs. Double bonds are stronger than single bonds and are same embodiment, though it may. Furthermore, the phrase more reactive. The term “triple bond refers to the sharing “in another embodiment as used herein does not necessarily of three electron pairs. As used herein, the term “ene-yne' refer to a different embodiment, although it may. Thus, as refers to alternating double and triple bonds. As used herein described below, various embodiments of the technology the terms “amine bond,” “thiol bond, and "aldehyde bond' may be readily combined, without departing from the scope 55 refer to any bond formed between an amine group (e.g., a or spirit of the technology. chemical group derived from ammonia by replacement of In addition, as used herein, the term 'or' is an inclusive one or more of its hydrogen atoms by hydrocarbon groups), “or operator and is equivalent to the term “and/or unless a thiol group (e.g., Sulfur analogs of alcohols), and an the context clearly dictates otherwise. The term “based on aldehyde group (e.g., the chemical group —CHO joined is not exclusive and allows for being based on additional 60 directly onto another carbon atom), respectively, and another factors not described, unless the context clearly dictates atom or molecule. otherwise. In addition, throughout the specification, the As used herein, the term “covalent bond' refers to the meaning of “a”, “an, and “the include plural references. linkage of two atoms by the sharing of two electrons, one The meaning of “in” includes “in” and “on.” contributed by each of the atoms. As used herein, the term “wavefront” refers to a line of 65 As used herein, the terms “optical anisotropy” and “bire demarcation that is observable between a region of ordered fringence” refer to the optical property of having a refractive liquid crystal and a region of disordered liquid crystal. In index that depends on the polarization and propagation US 9,575,037 B2 17 18 direction of light. Optically anisotropic materials are said to disklike (discotic). The ligand can be monodentate (e.g., be birefringent. The anisotropy in optical properties of liquid 4-substituted pyridines), bidentate (e.g., beta-diketonates, crystals gives rise to optical birefringence, that is, different dithiolenes, carboxylates, cyclometalated aromatic amines), refractive indices when measured with different polarization or polydentate (e.g., phthalocyanines, porphyrins). The directions. ligands influence the mesophase character based on molecu As used herein, the term “magnetic anisotropy” refers to lar shape and intermolecular forces. The metallomesogens having different magnetic properties for different directions provide a rigid core, which is typically unsaturated and of magnetic fields. Magnetic anisotropy produces different either rod- or disklike in shape, and several long hydrocar bon tails where the metal atom is usually at or near the center magnetic Susceptibilities in a material when measured with of gravity of the molecule. Metallotropic liquid crystals, different magnetic field directions. 10 acting through the metal moiety, can be tuned to capture As used herein, the term “dielectric anisotropy” refers to different target analytes by different methods including but having different dielectric properties for different directions not limited to displacement, redox reactions, and ligand of electric fields. Dielectric anisotropy produces different formation. dielectric constants in a material when measured with dif As used herein, the term "heterogenous surface” refers to ferent electric field directions. 15 a Surface that orients liquid crystals in at least two separate As used herein, the term “spectrum” refers to the distri planes or directions, such as across a gradient. bution of electromagnetic (e.g., light) energies arranged in As used herein, “nematic' refers to liquid crystals in order of wavelength. which the long axes of the molecules remain Substantially As used the term “visible spectrum” refers to light radia parallel, but the positions of the centers of mass are ran tion that contains wavelengths from approximately 360 nm domly distributed. Nematic liquid crystals can be substan to approximately 800 nm. tially oriented by a nearby surface. As used herein, the term “substrate” refers to a solid “Chiral nematic.' as used herein refers to liquid crystals object or Surface upon which another material is layered or in which the mesogens are optically active. Instead of the attached. Solid Supports include, but are not limited to, glass, director being held locally constant as is the case for metals, gels, and filter paper, among others. 25 nematics, the director rotates in a helical fashion throughout As used herein, the terms “array' and “patterned array' the sample. Chiral nematic crystals show a strong optical refer to an arrangement of elements (e.g., entities) onto or activity that is much greater than can be explained solely on into a material or device. For example, depositing several the bases of the rotatory power of the individual mesogens. types of liquid crystals into discrete regions on an analyte When light equal in wavelength to the pitch of the director detecting device would constitute an array. 30 impinges on the liquid crystal, the director acts like a As used herein, the term “in situ refers to processes, diffraction grating, reflecting most and sometimes all light events, objects, or information that are present or take place incident on it. If white light is incident on Such a material, within the context of their natural environment. only one color of light is reflected and it is circularly As used herein, the term “sample' is used in its broadest polarized. This phenomenon is known as selective reflection sense. In one sense it can refer to a biopolymeric material. 35 and is responsible for the iridescent colors produced by In another sense, it is meant to include a specimen or culture chiral nematic crystals. obtained from any source, as well as biological and envi “Smectic.' as used herein, refers to liquid crystals that are ronmental samples. Biological samples may be obtained distinguished from “nematics by the presence of a greater from animals (including humans) and encompass fluids, degree of positional order in addition to orientational order. Solids, tissues, and gases. Biological samples include blood 40 In a Smectic phase the molecules spend more time in planes products, such as plasma, serum and the like. Environmental and layers than they do between these planes and layers. samples include environmental material Such as Surface “Polar smectic’ layers occur when the mesogens have matter, soil, water, crystals, and industrial samples. These permanent dipole moments. In the Smectic A2 phase, for examples are not to be construed as limiting the sample example, successive layers show anti ferroelectric order, types applicable to the present technology. 45 with the direction of the permanent dipole alternating from As used herein, the term “liquid crystal” refers to a layer to layer. If the molecule contains a permanent dipole thermodynamic stable phase characterized by anisotropy of moment transverse to the long molecular axis, then the chiral properties without the existence of a three-dimensional Smectic phase is ferroelectric. A device utilizing this phase crystal lattice, generally lying in the temperature range can be intrinsically bistable. between the Solid and isotropic liquid phase. 50 “Frustrated phases,” as used herein, refers to another class As used herein, the term “mesogen' refers to compounds of phases formed by chiral molecules. These phases are not that form liquid crystals, including rod-like or disc-like chiral; however, twist is introduced into the phase by an molecules that are components of liquid crystalline materi array of grain boundaries. A cubic lattice of defects (where als. the director is not defined) exists in a complicated, orienta As used herein, “thermotropic liquid crystal refers to 55 tionally ordered twisted structure. The distance between liquid crystals that result from the melting of mesogenic these defects is hundreds of nanometers, so these phases Solids due to an increase in temperature. Both pure Sub reflect light just as crystals reflect X-rays. stances and mixtures form thermotropic liquid crystals. “Discotic phases” are formed from molecules that are disc “Lyotropic, as used herein, refers to molecules that form shaped rather than elongated. Usually these molecules have phases with orientational and/or positional order in a sol 60 aromatic cores and six lateral Substituents. If the molecules vent. Lyotropic liquid crystals can be formed using amphi are chiral or a chiral dopant is added to a discotic liquid philic molecules (e.g., sodium laurate, phosphatidyletha crystal, a chiral nematic discotic phase can form. nolamine, lecithin). The solvent can be water. "Metallotropic.” as used herein, refers to metal complexes Embodiments of the Technology of organic ligands that exhibit liquid crystalline character. 65 Thermotropic metallomesogens have been made that incor The present technology relates to detecting gaseous com porate many metals. They can be rodlike (calamitic) and pounds using a liquid crystal assay format and a device US 9,575,037 B2 19 20 utilizing liquid crystals as part of a reporting system. Liquid tion of the LC on a surface) that can be detected using a crystal-based assay systems and devices (LC assays) are variety of instruments capable of detecting these physical described, e.g., in U.S. Pat. No. 6,284, 197: Int’l App. Pub. changes. Nos. WO 2001/061357; WO 2001/061325; WO 1999/ In some embodiments, the LC molecules are oriented on 063329; Gupta et al. (1998) Science 279:2077-2080; Kim et a chemically functionalized surface having a Surface chem al. (2000) "Orientations of Liquid Crystals on Mechanically istry that is known to interact with the target analytes. When Rubbed Films of Bovine Serum Albumin: A Possible Sub the sensor Surface is exposed to a test environment, the strate for Biomolecular Assays Based on Liquid Crystals' analyte diffuses through the LC film and interacts with the Analytical Chemistry 72: 4646-4653; Skaife et al. (2000) surface chemistry. As a result, the orientation of the LC on “Quantitative Interpretation of the Optical Textures of Liq 10 the modified Surface changes, thus leading to a change in the uid Crystals Caused by Specific Binding of Immunoglobu optical properties of the LC film. lins to Surface-Bound Antigens' Langmuir 16:3529-3536; In some embodiments, the LC sensor comprises an LC Gupta et al. (1999) “Using Droplets of Nematic Liquid film that is supported by a single chemically functionalized Crystal To Probe the Microscopic and Mesoscopic Structure 15 surface and the whole LC film is exposed to the test of Organic Surfaces' Langmuir 15: 7213-7223; and Shah et environment. Upon exposure, the analyte molecules diffuse al. (2001) “Principals for Measurement of Chemical Expo through the LC film and bind to the surface chemistry and Sure Based on Recognition-Driven Anchoring Transitions in the LC molecules change orientation. As a result, the optical Liquid Crystals' Science 293: 1296-99, all of which are properties and appearance of the LC film change in real incorporated herein by reference. time. Depending on the Surface chemistry/analyte combina U.S. Pat. No. 6,284.197 and Shah et al. Supra, describe the tion, the response can be reversible or irreversible. This detection of chemical molecules with a liquid crystal assay embodiment allows for the sensitive detection of analytes. In format that relies on an orientational change in the LC Some embodiments, the dynamic response of the sensor is following the interaction of the chemical molecules with a monitored by measuring the response time (e.g., the time it functionalized surface on which the LC has been overlaid. 25 takes for the sensor to respond). The response time is a Moreover, liquid crystal assays are also used for detecting function of the concentration of the analyte and is used as a gaseous compounds that interact directly or indirectly with parameter to assess the quantitative response of the sensor. the LC itself to produce a phase transition of the LC Some embodiments utilize a thin film of LC supported material. The use of different LCs that provide different between two chemically functionalized surfaces with open functional moieties and/or reactive groups, or the use of LC 30 ings from one or more sides of the sensor. When the monitor compositions comprising a dopant, in the assays provide is exposed to the test environment, the analyte now will have to diffuse from the side of the sensor (as opposed to from the materials that identify gaseous compounds through the inter top of the LC film). Therefore, only the cross-section of the action of the gaseous compound with the functional moieties LC film is exposed to the test environment. As the analyte on the LC and/or the dopant. Furthermore, the liquid crystal 35 diffuses across the film, it interacts with the surface chem assay devices of the present technology find use to quantify istry, thereby inducing a change in the orientation of the LC. gaseous compounds. This change appears as a bright front on the sides of the In some embodiments, the detection of analytes or their sensor open to the test environment that propagates inward derivatives in gas phase is accomplished through a direct into the LC film as the exposure time increases. Because of interaction of the analyte with the LC. Depending upon the 40 the macroscopic diffusion dimension involved, the response target analyte, some embodiments provide LCs that are is irreversible and it provides a cumulative measure of the synthesized to have a functional group that specifically analyte. A measurable response is obtained after macro interacts or reacts with the analyte. The liquid crystal can scopic lateral diffusion of the analytes through the LC film. either be supported on a Surface or in a small bulk amount In some embodiments, the technology is related to detect through which the analyte is passed. The present technology 45 ing VOCs using materials and structures in conjunction with is not limited to the detection of any particular analyte in gas liquid crystals (LCs) that find use in simple, inexpensive phase. Indeed, the detection of a variety of analytes is sensors for unambiguous detection of VOCs. In particular, contemplated. Exemplary analytes are nitric oxide, formal changes in physical properties of a LC material in contact dehyde, and hydrogen sulfide. A number of LCs with with these materials and structures, upon exposure to VOCs, different functional moieties is commercially available. 50 are detected visually, by simple light intensity measurement, Some of these LCs have suitable reactive moieties that are or by measuring other measurable physical parameters (such selective for some target analytes. For example, MBBA as dielectric anisotropy, light scattering, etc.) associated with (N-(4-methoxybenzylidene)-4-butylaniline and EBBA (N- the state of LC material. (4-ethoxybenzylidene)-4-butylaniline) have functional I. Liquid Crystals groups similar to the aniline group that can be used for 55 The technology is related to sensors comprising a liquid detecting nitrate-based gases. A number of azomethine-type crystal (LC). The technology is not limited in the liquid LCs (see, e.g., Hioki et al. (2004) Tetrahedron Letters 45: crystal used and, further, the technology provides various 7591-7594), polyaniline-based polymers (J. Phys. Chem. B embodiments in which any known or yet discovered LC is 108: 8894-8899), and polyaniline-based moieties and poly used according to the technology as it is described herein. imides (Journal of Polymer Science. Part A. Polymer 60 Any compound or mixture of compounds that forms a Chemistry 40: 1583-1593) have been synthesized. The inter mesogenic layer can be used in conjunction with the present action between the analyte and the LC can be physical in technology. The mesogens can form thermotropic or lyo nature or based on a chemical reaction. The interaction of the tropic liquid crystals. The mesogenic layer can be either target analyte with the LC can manifest as a change in a continuous or it can be patterned. In some embodiments, the physical property of the LC (e.g., a change in the phase 65 LC comprises a compound comprising a Schiff base. In transition temperature, optical birefringence, dielectric Some embodiments, the compound is a diazo compound, an anisotropy, magnetic anisotropy, or a change in the orienta aZOXy compound, a nitrone, a stilbene, a tolan, an ester, or US 9,575,037 B2 21 22 a biphenyl. For example, in some embodiments, the LC II Devices comprises a compound according to the structure: Devices Comprising a Defined Headspace (i.e., Microfluidic Cells) In some embodiments, the devices according to the tech nology comprise a headspace to control diffusion of analytes above the LC. In this embodiment, the device comprises a Substrate having a micropillared area that is chemically functionalized with a surface chemistry that is specific for the target analytes. The micropillared area is filled with the wherein R and R' are independently selected from alkyl, 10 LC using capillary action to form a thin (e.g., approximately 1 to 20 microns, e.g., 5 microns) film. This sensor Substrate lower alkyl, Substituted alkyl, aryl groups, acyl, halogens, is then paired with a glass Substrate with a headspace (e.g., hydroxy, cyano, amino, alkoxy, alkylamino, acylamino, having a height of 1 to 100 microns, e.g., 20 microns) to thioamido, acyloxy, aryloxy, aryloxyalkyl, mercapto, thia, allow controlled diffusion of the targeted analytes above the aza, oxo, Saturated cyclic hydrocarbon, unsaturated cyclic LC film. In some embodiments, the headspace is variable. In hydrocarbons, heterocycle, arylalkyl, Substituted aryl, alky 15 Some embodiments, the first and second Surfaces form a lhalo, acylamino, mercapto, Substituted arylalkyl, het compartment having first and second open ends, wherein the eroaryl, heteroarylalkyl, substituted heteroaryl, substituted headspace at the first end is from 1 to 20 microns and the heteroarylalkyl, substituted heterocyclic, and heterocycli headspace at the second end is from 21 to 100 microns. In Some embodiments, the top surface is functionalized with calkyl. In some embodiments, X is selected from C1 to C10, (Tridecafluoro-1,1,2,2-tetrahydrooctyl)-trichlorosilane (OTS) on which the LC film does not spread. This minimizes or eliminates the forming and spreading of Small LC drop lets that could touch the top surface and obstruct the diffu In some embodiments the LC is a nematic LC (e.g., E7) sion of gas across the head space. This embodiment of the and in Some embodiments the LC is a Smectic liquid crystal 25 device provides sensitive detection of analytes in real-time (e.g., 8CB). In some embodiments, the LC is a thermotropic and provides a cumulative detection of analytes. Addition ally, in this embodiment, varying the thickness of the head LC and in some embodiments the LC is a lyotropic LC. space between the LC film and the OTS coated surface Additional examples of liquid crystals, include, but are not provides control of the dynamic range of the device. In some limited to, 4-cyano-4'-pentylbiphenyl (5CB) and 7CB. A embodiments, a spacer is placed between the two halves of large listing of Suitable liquid crystals is presented in “Hand 30 a sandwich type of a cell. In some embodiments, the spacer book of Liquid Crystal Research’ by Peter J. Collings and comprises a material Such as mylar or some polymer mate Jay S. Patel, Oxford University Press, 1997, ISBN 0-19 rial having a defined thickness. 508442-X, incorporated herein by reference. Devices Comprising a Channel The technology comprises use of polymeric liquid crys In some embodiments, devices according to the technol 35 ogy comprise a channel (e.g., a microfluidic channel) having tals in Some embodiments. In some embodiments, the LC is a functionalized surface. In contrast to these embodiments of a cholesteric liquid crystal and in some embodiments the LC the technology, some conventional LC sensors are fabricated is a ferroelectric liquid crystal. In some embodiments, the by Supporting a thin film of LC on a chemically function LC is Smectic C. Smectic C, a blue phase, and/or a Smectic alized surface. When these sensors are exposed to the A LC. It is further envisioned that LCs useful in the 40 environment to be tested, the analyte diffuses through the LC invention may further include additions of dopants such as, film and then interacts with the Surface chemistry to change but not limited to, chiral dopants as described by shitara H, the LC orientation. However, in these configurations (e.g., et al. (Chemistry Letters 3:261-262 (1998)) and Pape, M., with the LC film in place), the analyte has to diffuse through the LC film to reach the Surface chemistry. In some cases, et al. (Molecular Crystals and Liquid Crystals 307: 155-173 problems arise, especially with the sensitivity of the sensors. (1997)). The introduction of a dopant permits manipulation 45 For example, since the analyte has to diffuse through the LC of the liquid crystal’s characteristics including, but not film, the LC acts as a diffusion barrier that consequently limited to, the torque transmitted by the liquid crystal to an reduces the sensitivity of the device. As such, the sensitivity underlying Surface. Other dopants, such as salts, permit of detection is limited by the partition of the gas through the manipulation of the electrical double layers that form at the LC film. Additionally, if the analyte reacts with the LC, interfaces of the liquid crystals and thus permit manipulation 50 Some analyte is consumed before it reaches the active of the strength of anchoring of the liquid crystal at the Surface. interface. A number of methods for preparing interfaces Accordingly, provided herein are embodiments that between liquid crystals and aqueous phases lie within the address sensor sensitivity using a two-step process in which Scope of the present invention. An approximately planar the chemically functionalized surface is first exposed to the 55 analyte and then the LC is added to contact the modified interface can be prepared by a film of liquid crystal in Surface. The region that had been exposed to the analyte contact with an aqueous phase, or alternatively a curved exhibits a different LC orientation relative to the unexposed interface can be prepared by using a droplet of liquid crystal regions. This approach is, in particular, very effective if the dispersed in an aqueous phase. The scope of the invention is analyte irreversibly reacts with the surface chemistry. not limited by the methods by which interfaces between 60 In some embodiments, the technology is related to a aqueous phases and liquid crystals can be prepared by those microfluidic device. Embodiments of the device according skilled in the art. to the technology comprise well defined microchannels In some embodiments, the liquid crystals may preferably formed on a PDMS (polydimethylsiloxane) slab that is paired with a chemically functionalized Surface. The gas be selected from MBBA, EBBA, E7, MLC-6812, MLC 65 sample containing the analyte is flowed through the micro 12200, 5CB (4-n-pentyl-4'-cyanobiphenyl), 8CB (4-cyano fluidic channel defined between the PDMS slab and the 4'octylbiphenyl) and 4-(trans-4-heptylcyclohexyl)-aniline. chemically functionalized surface. After a predefined time, US 9,575,037 B2 23 24 the PDMS channels are removed and a thin film of LC is TABLE 1-continued overlaid between an OTS coated slide and the now-reacted chemically functionalized surface. The length of the channel Properties of LCs and amines that reacted with the analyte shows a different LC orientation Liquid Functional Ty (and thus appears different when interrogated by, e.g., polar- 5 Crystals Source Composition Group (° C.) ized light) compared with the background or with an unre SCB Merck cyano biphenyl nitrile 35 acted region of a channel. For a fixed flow rate and exposure E7 Merck cyano bi & terphenyls nitrile 65 time, the length of the channel having a changed LC TL. 205 Merck fluorinated bi & terphenyls fluorine 87 orientation is a function of concentration of the analyte. O Amines (Aldrich) Thus, by measuring the length of the channel having a 1 NH2 different LC orientation the concentration of the analyte is determined. This approach not only allows a sensitive detec tion of analytes, but also provides a quantitative method to determine an unknown concentration of an analyte. More 15 over, this approach provides efficient sampling of analytes Aniline by increasing the number of analyte molecules that come in NH2 contact with the chemically functionalized surface, thereby significantly improving the sensitivity of detection of gases. CH3 Dosimeters In some embodiments, the sensors find use in a dosimeter for, e.g., personal monitoring of a person to an analyte Such as a toxic gas (e.g., formaldehyde (HCHO), HS, NO, o-Toluidine organic compounds, etc.). For example, it is contemplated NH2 that some embodiments of the technology allow detection of as a concentration range of an analyte when exposed for a H3C particular amount of time, e.g., 0.15 to 10 ppm HCHO after 4-Butylaniline an 8-hour exposure. Devices are constructed and verified by NHNH exposing the dosimeters to analyte (e.g., HCHO gas) inside an exposure chamber by delivering the analyte at a known to concentration and flow rate (e.g., HCHO at a nominal flow ON NO2 rate of 200 ml/minute) to minimize the linear velocity (<1 2,4Dinitrophenylhydrazine cm/minute) at the dosimeter Surface and thus mimic a static exposure. After exposure, optical images of the dosimeter are captured using a digital camera and analyzed using is Exemplary properties of some mesogens are provided in image processing Software to measure the response, e.g., by Table 2 (phase transition temperatures T are provided in the decrease in light intensity (brightness) between the degrees Celsius). crossed polarizers or by the increase in the width of the dark Moreover, it is contemplated that the response to analyte front. varies with the thickness of the LC film. Accordingly, in While an understanding of the mechanism is not required a Some embodiments the devices comprise a micropillared to practice the technology, in some embodiments the sensi substrate (as described herein) that determines the thickness tivity of detection depends, for example, on the chemical of the LC film. For example, some embodiments comprise functionality of the LC composition and/or the thickness of micro-pillars having heights of 2, 5, or 10 microns as the LC film. For example, data collected during the devel produced using conventional photolithography. As opment of particular embodiments of the technology dem 45 described for the technology provided, substrates are filled onstrated a selectivity of MBBA, a LC known to significant with an LCs (e.g., as provided in Tables 1 or 2) using concentrations of 4-methoxybenzaldehyde and 4-butylani capillary action and the LC-filled substrates are paired with line, for selective detection of HCHO. The specificity of the a clean glass Substrate with a fixed head-space (e.g., 25 or 45 response of the MBBA-based LC to HCHO is consistent microns) to form a dosimeter badge. with the response being caused by a reaction between the 50 Various combinations of LC composition and film thick 4-butylaniline present in MBBA. This reaction, driven by ness are contemplated to provide various sensitivities to a mass action in the presence of HCHO results in a Schiffs number of analytes. In particular, different functional groups base compound that causes LC to undergo phase transition (e.g., for those embodiments that comprise a functional and the LC film appears dark when viewed between crossed group) provide for the specific detection of different ana polars. Accordingly, it is contemplated that other LCs having 55 lytes. The thickness of the LC is related to the rate of different compositions and chemical functionalities, when interaction of the analyte with the functional groups and the mixed with different amines provide sensitive detection of size of the headspace is related to the rate of exposure of the HCHO (Table 1). device to the analyte. The evolution of a dark front results in a decrease in the TABLE 1. 60 measured brightness. In some embodiments a change of at least 10% from an initial unexposed value is a response to Properties of LCs and amines analyte exposure. For example, as applied to the detection of Liquid Functional HCHO, preferred embodiments detect 0.15 ppm of HCHO Crystals Source Composition Group (° C.) after an 8-hour exposure. Fabricating embodiments com MBBA Aldrich schiff's base imine, 45 65 prising various combinations of LC, film thickness, and a ether defined headspace provide for control of the dynamic range of the devices. For example, some embodiments provide a US 9,575,037 B2 25 26 dynamic range of 0.15 to 10 ppm (e.g., as for some embodi and the phase transition in LC is denoted by a striking ments that detect HCHO) and some embodiments provide a change in optical appearance of the sensor (FIG. 33b). In dynamic range of 0.1 to 15 ppm (e.g., as for Some embodi other embodiments of the invention, the VOC causes a ments that detect HS). In some embodiments, the device change from one liquid crystalline phase into another liquid (e.g., a dosimeter) is exposed to sample on 1, 2, 3, 4, or more crystalline phase. It is not necessary that the phase transition edges while the remaining edges are sealed to prevent or involve an isotropic phase. minimize the entrance of analyte through those edges. The Detection Based on Structural Change of LC Confined in total Surface area of the LC exposed to a sample possibly Micro/Nano Structures comprising an analyte is related to the response of the device When a LC droplet is confined by a micro and/or a nano to the analyte. In some embodiments, the distance the dark 10 front travels in to the dosimeter is related to the response of structure, the LC molecules inside the droplet assume a the device to the analyte. well-defined configuration that is determined by the prop By testing embodiments of the devices using known erties of the material forming the structure, the dimensions amounts of analyte, a dose-response curve is produced that of the structure, and the LC materials. The absorption of correlate a measured response to an analyte concentration. 15 analyte molecules induces a change in the structure and After measuring the device response to an unknown con dimensions of the confining structure. The structural centration of analyte, the dose-response curve provides for changes in the confining material, in turn, induce a change the calculation of the unknown concentration from the in the ordering of the LC inside the cavity. By appropriate measured response. Statistical analysis of the response to selection of the materials for confinement, structures for known concentrations of analyte provides an estimate of the encapsulating LCs, and LC materials, the selectivity and error in a measurement of an unknown. sensitivity of detection is tuned. FIG. 34 shows a basic Testing the device response to potentially interfering principle behind this approach of detection where a LC compounds verifies the specificity of the response. For droplet is confined inside a polymer matrix that is known to example, devices specific for a particular analyte do not adsorb target analytes. In this example, the polymer material respond or have a minimal response to other Substances that 25 provides LC alignment perpendicular to the LC-polymer are not the analyte. In some embodiments, an LC and/or interface. The polymer matrix is confined between two rigid functional group is chosen that shows a maximal response to structures so that it can deform only along the one direction the target analyte and a minimal or no response to non-target (indicated by the arrow). Upon exposure to analyte, the Substances. Some embodiments comprise a filter (e.g., a polymer deforms to an anisotropic shape inducing an order membrane, adsorbent, Zeolite, etc.) to prevent or minimize 30 the response of the device to particular non-analyte Sub ing transition in the LC droplet. Various embodiments of the stances. In addition, dosimeters are tested to verify that same basic principle are envisioned. For example, one temperature changes and gas flow rate do not adversely embodiment involves fabrication of well-defined polymer affect the device performance. For example, some embodi dispersed LC structures that deform/change upon exposure ments provide a housing for the device that controls the flow 35 to an analyte such as a VOC. rate of the sampled environment to the sensing Surface. The Detection Based on Dewetting of Film Supporting LCs shape and configuration as well as the size of the aperture The stability of a thin film of material deposited on a solid that allows the passage of sample gas to access the LC Substrate depends on a number of parameters such as the device are related to the control of the flow rate. Surface energy of the Substrate, the physical and chemical Some embodiments provide a device that is responsive to 40 structure of the deposited material, the thickness of the film, Several Substances, e.g., a class of compounds (e.g., organic, etc. Some polymeric materials such as polystyrene form a aliphatic, aromatic, halogen, etc.) or particular functional stable film on glass or silicon. The PS film has been shown groups. to dewet if the thickness of the film is lower than a critical III Detection value or if the temperature of the film is raised above a Detection Based on Phase Transition 45 critical value. Since the effect of exposing a polymer film to LC materials typically comprise rod-shaped organic mol analytes (e.g., a VOC Such as toluene) is very similar to ecules. These molecules form anisotropic condensed phases heating (e.g., exposure to toluene lowers the glass transition that possess long-range orientational ordering (crystal-like) of polymer), it is anticipated that exposure to Some analytes but lack positional ordering (liquid-like). The long-range will induce the dewetting of the film. If the underlying ordering of molecules within an LC gives rise to anisotropic 50 substrate and the polymer materials are selected so that the optical properties—so-called optical birefringence. Absorp orientation of LC on the substrate relative to the orientation tion of analytes (e.g., VOCs) into the LC phase disrupts the of LC on the substrate coated with polymer is different, long-range order of the LC, thus giving rise to a phase exposure to analyte will lead to a change in the orientation transition to an isotropic material. This phase transition, in of the LC. The sensitivity of detection can be enhanced by turn, leads to distinct changes in the optical appearance of 55 selecting polymer material that has a high absorption of the LC. FIG. 33 illustrates the principles underlying the LC analytes of interest. The basic principle behind the dewet sensor for detection of analytes using a phase transition. The ting-induced orientational transition is schematically shown sensor comprises a micrometer-thick film of LC Supported in FIG. 35. The main difference between the analyte-induced on a solid Substrate decorated with polymeric micro-pillars orientational transition and the dewetting approach is that in (5um diameter, 10um center-to-center spacing). The micro 60 an analyte-induced orientational transition the LCs remain in pillars are used to form mechanically robust thin films of the contact with the chemically functionalized surface before LC. Prior to exposure to toluene, the LC possesses a bright and after exposure. In this approach, the chemically func visual appearance between crossed polarizers. When the tionalized surface (in this case polymer) is modified and sensor is exposed to the test environment containing ana physically dewets the substrate. As a result, the LC comes in lytes, analyte molecules rapidly diffuse into the LC film 65 contact with the underlying Surface. The film that undergoes (FIG. 33a) to induce a nematic-to-isotropic phase transition. the dewetting transition can be formed from a number of The process of diffusion into the LC is rapid, predictable, organic or inorganic materials. US 9,575,037 B2 27 28 Detection Based on Changes on Microscopic Structures on Detection Based on Orientational Transition Induced by a Polymer Film Supporting LC Film Localized Concentration at Defect Sites in LC The orientation of an LC at the LC-substrate interface is In some embodiments, a thin film of LC is Supported on extremely sensitive to changes in physical and chemical a locally rough Surface (for example etched silicon dioxide) properties of the LC-substrate interface. Rubbed polymer 5 that possesses sharp defects while promoting well defined (such as polyimide) films have been widely used in LC orientation (for example, an orientation that is Substantially display industries to achieve uniform planar alignment of perpendicular to the surface) of the LC. When this film of LCs. Although the exact mechanism for the rubbing-induced LC is exposed to an environment containing an analyte (e.g., LC alignment is not fully understood, it is believed that VOCs), the analyte molecules diffuse through the film of LC 10 and concentrate locally at the defect sites. When the local anisotropic physical interactions related to anisotropy in concentration of analyte at the defect site is greater than the Surface morphology are responsible for uniform alignment threshold needed to induce an orientational transition, the of LCs on rubbed polymer surfaces. However, an under LC film undergoes the orientational transition (FIG. 38). standing of the mechanism is not required to practice the Related embodiments involve the use of a blue phase of a technology. Polymer materials, that are known to cause 15 LC that is known have defect states in the film itself (as swelling as a result of VOC absorption, can be deposited on opposed to the defect being in the Surface Supporting the a solid Substrate and mechanically sheared to generate film). These defect states concentrate the analyte molecules micro-structures similar to those used for LCD displays. locally to induce melting at these defect sites. These Surfaces initially promote uniform alignment of LCs. Detection Based on Swelling of Polymer Beads Dispersed in Absorption of analytes such as, e.g., VOCs, induces struc LC tural changes at the LC-Surface interface. This structural In some embodiments, micro and/or nano Scale polymer change leads to a change in the orientation of the LC film. beads composed of materials that are known to swell by This principle was used (see FIG. 36) to achieve a uniform absorbing certain analytes (e.g., VOCs) are suspended in the alignment of LC on Surfaces coated with polymer films, e.g., LC matrix. The dimension of the beads is small enough not films formed from poly(vinyl acetate) (PVAc) and polysty 25 to distort the LC director when they are suspended. The LC rene (PS). It is contemplated that a polymeric or liquid is uniformly aligned and the LC film does not scatter light. crystalline polymeric film can be stabilized (e.g., thermally, When this film is exposed to an environment containing electrically, or mechanically) in a thermodynamic non analyte, the beads Swell significantly due to absorption of equilibrium state. In Such a state, the film, upon exposure to analyte molecules. Once a dimension of the beads exceeds 30 a critical value the beads distort the director distribution in analyte, relaxes to a lower energy state by releasing the the LC matrix. As a result of distortion in the director stored energy. As a result, the LC film supported on this film configuration, the LC film scatters light (FIG. 39). An undergoes orientational transition. extension of this approach is to use beads that are randomly Detection Based on Dissolution of Ionic Compounds distributed in the LC matrix. When the LC film with beads Controlling the presence of ionic compounds in an LC 35 is exposed to an analyte, the density of the beads decreases provides a functionality to detect analytes. Two approaches (they become lighter) and they subsequently float on the top are contemplated. First, in Some embodiments, the presence of the LC surface. If the beads are chosen to be opaque they of certain ionic compounds in the LC induces a LC orien will block the light transmitted through the LC film. tation change at the LC-Surface interface. For example, a Detection of Gas Phase Compounds Surface prepared with tetrabutylammonium perchlorate was 40 The present technology provides methods and devices for shown to induce a homeotropic alignment as it dissolved the detection of gas phase compounds in a sample. The only into the LC layer. As the molecular weight and chain lengths limitations on size and shape are those that arise from the of the quaternary ammonium compounds increases, their situation in which the device is used or the purpose for solubility in non-polar solvents (e.g., toluene) increases. An which it is intended. In some embodiments, the devices LC film Supported on an appropriate quaternary ammonium 45 comprise a single Substrate that is open to the environment salt coated Surface is thus anticipated to dissolve this salt on one surface. The device can be planar or non-planar. The upon toluene exposure and produce a change in the LC device can be cylindrical in shape and in a linear or coiled orientation. Second, in Some embodiments, a cyanobiphenyl format, and with one or two ends of the device open to the LCs (e.g., 5CB, E7) aligns perpendicularly on Surfaces environment. Furthermore, it is within the scope of the 50 present technology to use any number of polarizers, lenses, decorated with bivalent and trivalent metal perchlorate salts. filters, lights, and the like to practice the present technology. Besides perchlorate salts, only a few other metal salts, such In some embodiments, devices comprise a mesogen. The as tetraphenylborate (a metal salt compressing a bulky present technology is not limited to any particular mecha anion), align LC perpendicular to the Surface. In addition, nism of action. Indeed, an understanding of the mechanism these salts with large anions possess high solubility in 55 of action is not necessary to practice the present technology. toluene or other non-polar organic solvents. In contrast to Nevertheless, it is contemplated that the in some embodi the metal perchlorate salts, bivalent and trivalent metals with ments the mesogens forming the liquid crystal of the devices anions such as acetate, chloride, nitrate, etc. are insoluble in of the present technology have an affinity for the targeted non-polar solvents and are known to align LCs parallel to the compound. This affinity causes a phase transition of the Surface. Thus, a Surface can be prepared from a mixture of 60 liquid crystal in the presence of the target. Particular meso metal tetraphenylborate and a metal acetate salt in an gens will transition from a higher order to a lower order adequate ratio to induce a homeotropic alignment initially. following interaction with different molecules. The devices As the surface is exposed to analytes such as a VOC the of the present technology are designed so that when gas tetraphenylborate is anticipated to enter into the LC layer phase compounds are present in a sample, the gas can enter followed by a LC orientation change due to a change in the 65 detection regions of the device where mesogens are arrayed Surface composition. A schematic of the principle is shown and cause a change in the phase order of the mesogen by in FIG. 37. interacting with the mesogen. This phase transition may be US 9,575,037 B2 29 30 from one phase selected from the group consisting of an strates. In some embodiments, the glass spacer rods range isotropic phase, a nematic phase, and a Smectic phase to from about 5 uM to about 100 uM, preferably about 25uM, another phase selected from the group consisting of an in thickness. It has been found that UV-curable adhesives are isotropic phase, a nematic phase, and a Smectic phase. The preferable as in Some instances the adhesive tape reacts with phase transition induces a change in the liquid crystal (e.g., the liquid crystal. a nematic region as opposed to an isotropic region) that can In further embodiments, the Substrates are arranged in a be detected in a variety of ways. housing. The housing can comprise any suitable material, In some embodiments, the present technology provides and is preferably made of polymeric material, for example, Substrates overlaid with mesogens into which the gas phase a plastic. In preferred embodiments, the housing is sealed to compound diffuses leading to a phase transition of the 10 mesogen. In other embodiments, the gas phase compound the environment except for an opening adjacent to the interacts directly with a reactive moiety of the mesogen to detection region or regions. The opening preferably allows induce the phase change of the mesogen. In still other diffusion of air to the detection region. In some embodi embodiments, the gas phase compound diffuses into a meso ments, the opening allows introduction of a liquid sample gen composition containing a dopant and interacts with a 15 wherein gas emitted from a constituent in the sample reactive moiety on the dopant leading to a phase transition impinges on the Substrates and can be interrogated. In some of the mesogen. In some embodiments, the gas phase embodiments, the opening is covered with a filter material compound interacts with a surface (e.g., a functional group that allows diffusion of air to the detection region, but does attached to the Surface) Supporting the mesogen Such that the not allow entry of particulate matter Such as dust, dirt, liquid, interaction of the gas phase compound with the Surface and insects into the detection region. In some embodiments, produces a change in orientation of the mesogen. the filter is an aerosol filter that substantially prevents the Accordingly, in some embodiments, the present technol introduction of aerosols into the detection region, but allows ogy provides Substrates comprising at least one detection an analyte in vapor form to enter the detection region. In still region comprising a mesogen composition comprising a more preferred embodiments, the devices comprise two or reactive moiety that binds to or otherwise interacts with a 25 more filters positioned so as to allow air exchange though gas phase compound. In some embodiments, the detection the device, and in particular, through the detection region. regions are discrete and created by arraying at least one For example, the filters can be arranged at either end of the reactive moiety on the surface of the substrate. In some detection region. In further embodiments, the housing is embodiments, a plurality of mesogens with various reactive moveable between an exposure mode and a reading mode. moieties is arrayed on the surface of the substrate so that 30 multiplexed assays for a variety of gas phase compounds can In the exposure mode, the detection regions are exposed to be conducted or so that different interactions with a variety the environment, while in the reading mode, exposure to the of reactive moieties can be used as a signature for a environment is Substantially or completely eliminated. It is particular gas phase compound. In some embodiments, a envisioned that after the device has been exposed to the liquid handler is used to deposit the mesogen composition in 35 environment, the housing can be moved to the reading mode the detection region. to prevent further exposure to the environment prior to In some embodiments, a second Substrate is provided that readout. is configured opposite the first Substrate so that a cell is In still further embodiments, the devices of the present formed. In some embodiments, the second substrate is also technology comprise a unique identifier. In some embodi arrayed with a mesogen composition comprising a reactive 40 ments, the unique identifier is a bar code. In other embodi moiety, while in other embodiments, the second substrate is ments, the unique identifier is an RFID chip. It is contem free of reactive moieties. In some embodiments, the meso plated that the unique identifier can provide information gen compositions comprising a reactive moiety are arrayed Such as a serial number, user identification, Source identifi on the first and second substrates so that when the first and cation, and the like. second Substrates are placed opposite each other the arrays 45 In use, the device is placed in an area where the gas phase match to form discrete detection regions. compounds are Suspected of being present. The device is In some embodiments, the cell that is formed by the first allowed to remain in place for a period of time (the exposure and second Substrates includes a space between the first and period, e.g., from one or more minutes to one or more hours second Substrates. In some embodiments, the space is to one or more days to one or more weeks or more). formed by placing a spacer (e.g., in Some embodiments 50 In other uses, a liquid sample that is biological or phar made of mylar) between the first and second substrates. In maceutical in nature and Suspected of containing bacteria is some embodiments, the space is then filled with the desired introduced into the device. The sample is allowed to incu liquid crystal. In still other embodiments, the substrates are bate for a period of time (e.g., for the exposure period, e.g., arranged so that a sample can interact with or enter into the from 15 minutes to 4 days). In a preferred use, the device detection regions. In some embodiments, the Substrates are 55 receives a liquid sample and is incubated at 37°C. for 1 hour fixed (e.g., permanently or removably) to one another. The with shaking to permit replication of bacteria that leads to present technology is not limited to any particular mode of release of metabolic gases. fixation. Indeed, a variety of modes of fixation are contem Following the exposure period, the cell is assayed for plated. In some embodiments, the Substrates are fixed to one whether a change in the liquid crystal phase has occurred another via adhesive tape. In preferred embodiments, the 60 over one or more of the detection regions. Although many adhesive tape is 8141 pressure sensitive adhesive (3M, changes in the mesogenic layer can be detected by visual Minneapolis, Minn.). In other embodiments, the substrates observation under ambient light, any means for detecting the are fixed to one another via a UV curable adhesive. In some change in the mesogenic layer can be incorporated into, or preferred embodiments, the UV curable adhesive is PHO used in conjunction with, the device. Thus, it is within the TOLEC(R) A704 or A720 (Sekisui, Hong Kong). In some 65 Scope of the present technology to use lights, microscopes, embodiments, glass spacer rods are utilized with the UV spectrometry, electrical techniques and the like to aid in the curable adhesive to provide spacing between the two sub detection of a change in the mesogenic layer. In some US 9,575,037 B2 31 32 embodiments, the presence of gas phase compounds is atmospheric Sample, or is exposed to an area suspected of detected by a change in the color and texture of the liquid containing or Susceptible to containing gasoline vapor. The crystal. presence of gasoline vapor is indicated by a phase transition Accordingly, in those embodiments utilizing light in the of the liquid crystal in the device. The phase transition may visible region of the spectrum, the light can be used to be observed visually or detected by a method such as simply illuminate details of the mesogenic layer. Alterna measurement of change in optical anisotropy, magnetic tively, the light can be passed through the mesogenic layer anisotropy, dielectric anisotropy, and measurement of phase and the amount of light transmitted, absorbed, or reflected transition temperature. can be measured. The device can utilize a backlighting Reflection-Based Probing device such as that described in U.S. Pat. No. 5,739,879, 10 Some embodiments of devices according to the technol incorporated herein by reference. Light in the ultraviolet and ogy comprise a Fabry-Perot filter. The present technology is infrared regions is also of use in the present technology. In not limited to a particular mechanism. Indeed, an under other embodiments, the device, and in particular the detec standing of the mechanism of the present technology is not tion region, is illuminated with a monochromatic light needed to practice the technology. Nevertheless, when elec source (e.g., 660-nm LEDs). In some embodiments, the cell 15 tromagnetic radiation propagates through an interface is placed in between cross-polarized lenses and light is between two dielectric media it undergoes reflection at the passed though the lenses and the cell. In still other embodi interface. If a dielectric material is sandwiched between two ments, the detection region is masked off from the rest of the highly reflecting mirrors forming a cavity, multiple reflec device by a template or mask that is placed over the device. tion of radiation occurs in the cavity. For a given thickness The devices of the present technology are useful for and dielectric properties of the cavity, the reflected electro measuring cumulative exposure to gas phase compounds. In magnetic radiation interferes constructively and shows a Some embodiments, cumulative exposure is assayed by maximum at a particular wavelength. The wavelength at determining the advancement of a wavefront in the detection which the reflected radiation shows a peak in intensity region. It is contemplated that the wavefront advances from depends on the thickness of cavity and the dielectric prop an opening associated with the detection region. The dis 25 erty of the cavity. When the refractive index of the cavity tance of advancement correlates to the degree of exposure to changes, the wavelength at which the maximum reflection gas phase compounds and is thus quantitative. In particular, occurs also changes. In some embodiments, the mirrors are it is contemplated that the rate of progress of the wavefront functionalized with receptors or other moieties that interact into the detection region depends on the concentration of gas with the specific analyte and binding of the target induces an phase compound to which the device is exposed. In some 30 orientational transition of the LC and hence a change in the embodiments, the front movement in millimeters is plotted dielectric property of the cavity. This change in the dielectric against elapsed time in hours. The resulting plot obeys a constant results in a shift in the wavelength at which the linear fit (preferably with a coefficient of correlation of reflected intensity is maximal. In some embodiments, the greater than 0.95) that is characteristic of the concentration analyte interacts directly with the LC to effect a change in of a gas phase compound in the sample (e.g., local atmo 35 the dielectric properties of the cavity. sphere). In some embodiments, wavefront advancement is In some embodiments, the Fabry-Perot filter devices measured by capturing a digital image or video in real time comprise a first Surface (e.g., an interior Surface) displaying of the detection region and determining the area and length one or more mesogen compositions. In some embodiments (e.g., in pixels) of the wavefront relative to the opening. In the mesogen composition comprises a reactive moiety. In Some preferred embodiments, the image is analyzed with an 40 Some embodiments, the Surface is reflective. In some image manipulation and analysis program Such as Image.J embodiments, the first Surface is gold. In some embodi (NIH). The pixels can then be converted into a distance in ments, the gold is deposited on a Supporting Substrate. Such millimeters if necessary. In other embodiments, the image is as glass or silicon. Other suitable substrates are described in analyzed by converting the image with a % white command more detail above. In further embodiments, the devices so that the area in which the liquid crystal has been disrupted 45 comprise a second Surface coated in a reflective material, by the gas phase compound appears white. The degree of preferably gold. In some embodiments, the second Surface advancement of the wavefront can be determined by mea also displays one or more mesogen composition. In some Suring pixel intensity and determining the point of image embodiments, the mesogen comprises a reactive moiety. In drop-off from high intensity (white) to low intensity (black). Some embodiments, the first and second Surfaces are con The devices of the present technology can also be used to 50 figured opposite one another to form a chamber there identify particular gas phase compounds. In some embodi between. Preferably, the chamber is fillable with a liquid ments, the detection region of the device comprises an array crystal. Some mesogens that find use in forming the liquid of at least two different mesogens. The pattern of response crystal are listed above and include, but are not limited to, to the at least two different mesogens can be used to identify E7, MLC-6812, MLC 12200, MBBA, EBBA, 5CB (4-n- particular compounds. 55 pentyl-4'-cyanobiphenyl), and 8CB (4-cyano-4'octylbiphe In some embodiments, gasoline vapor, or a component of nyl). gasoline vapor such as octane, is detected by phase transition In some embodiments, at least one mesogen composition of a liquid crystal. In some preferred embodiments, devices is deposited or otherwise interacts with the first or second for detecting gasoline vapor comprise at least one Surface in Surfaces. In some embodiments the mesogen comprises a contact with a liquid crystal composition, wherein the liquid 60 reactive moiety. The present technology is not limited to any crystal composition. In some embodiments, the liquid crys particular reactive moiety. Indeed, a variety of reactive tal composition comprises a mesogen selected from the moieties may be utilized, including, but not limited to, group consisting of MBBA, EBBA, E7, MLC-6812, MLC organic functional groups such as amines, carboxylic acids, 12200, 5CB (4-n-pentyl-4'-cyanobiphenyl), 8CB (4-cyano drugs, chelating agents, crown ethers, cyclodextrins, or a 4'octylbiphenyl) and 4-(trans-4-heptylcyclohexyl)-aniline. 65 combination thereof, a biomolecule Such as a protein, an In some embodiments, the device is exposed to a sample antigen binding protein such as a monoclonal antibody, a Suspected of containing gasoline vapor, for example an polyclonal antibody, a chimeric antibody, a humanized anti US 9,575,037 B2 33 34 body, a Fab fragment, a single chain antibody, etc., a peptide, a liquid crystal. In some embodiments, the first Surface is a nucleic acid (e.g., single nucleotides or nucleosides, oli spherical and a second Surface and chamber are formed as gonucleotides, polynucleotides, and single and higher described for the cylinder embodiments. Stranded nucleic acids) or combinations thereof. In other embodiments, the devices of the present technol The present technology is not limited to any particular ogy form a rugate filter. Again, the present technology is not Substrate shape. Indeed, a variety of Substrate shapes are limited to a particular mechanism. Indeed, an understanding contemplated, including, but not limited to, discs, cylinders, of the mechanism of the present technology is not needed to and spheres. Disc shaped devices are preferably configured practice the technology. Nevertheless, as the electromag as described above, with a single planar Surface that is netic radiation propagates through a number of interfaces overlaid with a liquid crystal. In some embodiments, the 10 between dielectric layers, multiple reflections occur at each discs have a diameter of between about 0.1 mm to 10 cm, interface and a portion of the radiation is transmitted and a e.g., about 1 mm to about 100 mm. In some embodiments, portion of it is reflected. If the dielectric constant of the highly reflecting mirrors are prepared by depositing ~500 medium exhibits sinusoidal variation, then the reflected nanometer thick gold films on clean glass slides (or plastic intensity shows a peak in the reflected intensity at a wave films) using an electron beam evaporator. In further embodi 15 length that depends on the average dielectric constant and ments, gold mirrors are layered with mesogens that provide the amplitude of sinusoidal variation of dielectric constant. a reactive moiety. In some embodiments, glass fiber rods The position of the reflected peak in the electromagnetic (e.g., approximately 25-micron diameter) mixed in isopro spectrum shifts as the average refractive index of the sinu panol are sprayed uniformly over one of the functionalized soidal variation changes. Accordingly, in some embodi mirrors. These rods act as spaces defining the thickness of ments, a sinusoidal variation in the dielectric property is the dielectric cavity. An optical cell is fabricated forming a created by fabricating porous silicon with sinusoidal poros cavity between two reflecting mirrors. In some embodi ity gradient along the depth. See, e.g., Li et al. (2003) ments, the mirrors are glued together using UV curable Science 299: 2045-47: Seals et al. (2002).J. Applied. Phys. adhesives. The cavity is then filled with a liquid crystal such 91(4): 2519-23; Schmedake et al. (2002) Adv. Mater. 14(18): as 4-n-pentyl-4'-cyanobiphenyl (5CB). The present technol 25 1270-72; Link et al. (2003) Proc. Nat'l Acad. Sci USA ogy is not limited to a particular mechanism of action. 100(19): 10607-10, all of which are incorporated herein by Indeed an understanding of the mechanism of action is not reference in their entirety. When the pores are filled with necessary to practice the present technology. Nevertheless, LCs, the LCs take on a specific phase. Upon exposure to the without exposure to the target analyte, the liquid crystals target analyte the LC undergoes a phase transition, which assume one phase (e.g., nematic). In some embodiments, the 30 induces a change in the dielectric constant of the pores mirror assembly is placed in the path of the light in a resulting in a shift in the position of the peak. spectrometer. For the optimized thickness, a peak appears in The present technology is not limited to the use of any the transmitted intensity at a particular wavelength deter particular type of silicon Substrate. In some embodiments, mined by the ordinary refractive index of the LC materials. the silicon Substrate is a p-type, boron-doped silicon wafer In some embodiments, upon exposure to an analyte, the 35 with about a 1 mOhm-cm resistivity. In some embodiments liquid crystal undergoes a phase transition (e.g., isotropic). the silicon wafer is polished. In some embodiments, the In some preferred embodiments, the device is placed in a silicon Substrate is ultrasonicated in isopropanol and then light path. A peak appears at a wavelength that corresponds rinsed with water. In some embodiments, the silicon wafers to the average refractive index of the nematic phase. The are etched using an anodization-etching process with a shift in the peak position of the transmission spectrum 40 mixture of 48% hydrofluoric acid and absolute ethanol (1:3 indicates a change in the refractive index of the cavity by volume) in a polytetrafluoroethylene (e.g., “Teflon’) cell caused by the phase transition of the liquid crystal that is using a sinusoidally modulated current density to generate a induced by interaction of the analyte with mesogen and/or sinusoidal variation in the porosity gradient. In further with the reactive moieties of the mesogen on the Surface. embodiments, the amplitude, period, and duration of the In some embodiments, hollow polymer cylinders (about 45 sinusoidal current density are adjusted to achieve the opti 100 to 1000 microns in diameter, e.g., about 500 micron in mum porous size and distribution. It will be recognized that diameter, about 1 mm to 1 cm in length, e.g., about 5 mm these parameters can be varied and optimized for the detec in length) are first coated with a reflective material such as tion of different analytes. In still further embodiments, the gold. In some embodiments, the coating is from about 50 to current density is then ramped up so that a freestanding film about 1000 nm in thickness, e.g., about 500 nm thick. A 50 of the porous silicon is detached from the substrate. spacer is then formed on the cylinder. In some embodiments, In still further embodiments, devices such as those the spacer is from about 50 to about 200 microns in described above are irradiated with electromagnetic radia thickness, e.g., about 25 microns. In some embodiments, the tion from the radio frequency region, including, but not spacer comprises glass fiber rods with a diameter of 25 limited to, frequencies between 1 KHZ and 10 THz, and microns (such as from EMIndustries) or plastic micropearls 55 including the VLF, LF, MF, HF, VHF, UHF, SHF, and EHF (spheres) of diameter 25 micron (such as from Sekesui regions of the radio spectrum. Studies have demonstrated Chemicals, Hong Kong). In some embodiments, these spac that analysis of the reflection and/or transmission spectra of ers are mixed in isopropyl alcohol and then sprayed onto the RF radiation can be used to identify analytes. See, e.g., U.S. cylinders. A -25-micron sacrificial layer of photoresist is Pat. Appl. 2004086929; Choi et al., Intl. J. High Speed then coated to these cylinders. Examples of useful photore 60 Electronics and Systems 13(4): 937-950 (2003); van der sist layers include, but are not limited to SU8 2010 from Weide, Springer Series in Optical Sciences (2003), 85:3 Michochem. Another thin nanoporous layer of gold is 17-334 (2003), all of which are incorporated herein by deposited on top of the sacrificial layer. The gold film with reference. In some embodiments of the technology, a change nanopores is strongly reflecting but allows Small molecules in phase of a liquid crystal gives rise to a change in the to penetrate through it. The sacrificial layer is then dissolved 65 reflection or transmission spectra of RF radiation. In further in acetone. The spacers in between two gold Surfaces act as embodiments of the technology, the frequency of the radia supporting struts. These hollow cylinders are then filled with tion is in the 0.1 to 10 THz range. Methods known to those US 9,575,037 B2 35 36 skilled in the art are used to analyze the radiation returned (Eu(TTA)3.H2O): etc., when dissolved in a liquid crystal to a detector following interaction with the liquid crystal. emit visible light upon exposure to UV radiation. The Photoluminescence intensity and the wavelength of the emitted light depend on In some embodiments, a liquid crystal phase transition is the orientation of the dye molecules with respect to liquid detected by photoluminescence. The present technology is crystal phase. If the dye molecules are immobilized on a not limited to a particular mechanism of action. Indeed, an Surface in a fixed orientation with respect to the Surface and understanding of the mechanism of action is not necessary the liquid crystal undergoes a phase transition, the charac to understand the present technology. Nevertheless, when teristics of the emitted radiation change. When an analyte silicon with a nanometer scale porous structure is exposed to interacts with the LC (e.g., directly or binds to a moiety Such electromagnetic radiation having a short wavelength, typi 10 as receptor on the LC mesogens), the liquid crystal under cally in the ultraviolet region, electron-hole pairs are cre goes phase transition and the wavelength of the emitted light ated. These excess carriers Subsequently recombine and emit changes. electromagnetic radiation. As the characteristic size of the Accordingly, in Some embodiments, a thin gold film is structures in the porous silicon decreases to the nanometer deposited on a Substrate (e.g., a UV-transparent quartz scale, the band gap of the silicon nanostructures progres 15 Substrate or a plastic film) using an electron beam evapora sively widens. The recombination of these quantum con tor. The gold Surface is assembled into a liquid crystal assay fined carriers (electron-hole pair) in the wide band gap device using Small glass spacer rods as described above. The causes emission of electromagnetic radiation in the visible device is then filled with a liquid crystal. In some embodi region. The wavelength of the emitted light depends on the ments, the LC provides a reactive moiety. The present dielectric constant of the materials filling the pores and the technology is not limited to any particular mechanism of structure of the pores themselves. When the surfaces of the action. Indeed, an understanding of the mechanism of action pores are filled with the liquid crystal, the liquid crystal takes is not necessary to understand the present technology. Nev on one phase (e.g., nematic). The porous silicon then emits ertheless, without exposure to the target analyte, the liquid light at a wavelength that corresponds to the radial distri crystal takes on one phase, for example, nematic. In some bution of the liquid crystal molecules. When the target 25 embodiments, the optical cell is irradiated with UV light, analyte binds to the mesogen or to reactive moieties on the which in some embodiments is provided by a laser. In the mesogens filling the pores, the liquid crystal undergoes a absence of the analyte, the fluorescent molecules emit vis phase transition (e.g., to isotropic) causing a change in the ible light at a wavelength that corresponds to the nematic dielectric constant. This results in a change in the position of phase of liquid crystals. When the device is exposed to an the peak. It will be recognized that the present technology is 30 analyte the liquid crystal undergoes a phase transition to, for not limited to any particular type of change in liquid crystal example, an isotropic phase. The shift in the peak position phase and that the described change from nematic to iso of the fluorescence spectrum (e.g., a change in the color of tropic is exemplary. Other changes are also contemplated, the emitted light) indicates a change in the dielectric envi including, for example, from Smectic to nematic or changes ronment of the fluorescent molecules. This change is caused in the amount of twist, where, for example, cholesteric liquid 35 by the phase transition of the LC induced by the analyte crystals are utilized. interacting with the mesogens or by binding of the analyte In some embodiments, porous silicon Substrates are fab to a reactive moiety on the mesogen. ricated and functionalized as described above. In further In other embodiments of the technology, fluorescent dye embodiments, the porous silicon is illuminated by a UV molecules such as Acridine Orange Base; Rhodamine 6G, light. The exact wavelength of the UV light depends on the 40 perchlorate, 5-decyl-4,4-difluoro-4-bora-3a,4a-diaza-s-in actual pore size, pore size distribution, and the refractive dacene-3-propionic acid; Nile Red: N,N'-Bis(2,5-di-tert-bu index of the liquid crystal material. The photoluminescence tylphenyl)-3,4,9,10-perylenedicarboximide; etc., are dis of the porous silicon is measured using a UV-visible spec Solved into the liquid crystal forming a guest-host system. trophotometer. The spectrum shows a peak at a wavelength The present technology is not limited to any particular corresponding to the phase of the liquid crystal. In some 45 mechanism of action. Indeed, an understanding of the embodiments, the porous silicon is exposed to the target mechanism of action is not necessary to understand the analyte in a closed chamber. The present technology is not present technology. Nevertheless, the orientation of the dye limited to any particular mechanism of action. Indeed, an molecule, in general, is dependent on the phase of the LC in understanding of the mechanism of action is not necessary the LC cell. When a beam of light (typically in the visible to understand the present technology. Nevertheless, as the 50 region) having a polarization parallel to the transition dipole target analyte binds to the mesogens or to a reactive moiety moment of the dye, is passed through the guest host system, provided by the mesogen on the surface of the pores, the LC the incident light energy is absorbed by the dye molecule. undergoes a phase transition. It is contemplated that the The dye molecules then emit (e.g., visible) light at a different change in the phase of the liquid crystal corresponds to a wavelength. However, if the incident light is polarized change in the spectrum of radiation emitted by the porous 55 perpendicularly to the transition dipole moment of the dye silicon. molecule, it is not absorbed and the dye molecules do not Fluorescence Based Detection emit any radiation. Therefore, in the absence of the target In some embodiments, detection is accomplished using a analyte, when the guest-host system is interrogated by a fluorescent reporter system. The present technology is not polarized light corresponding to the excitation wavelength limited to any particular mechanism of action. Indeed, an 60 of the dye used, the light emitted from the system is understanding of the mechanism of action is not necessary composed of the excitation wavelength. If the analyte is to understand the present technology. Nevertheless, certain present in the ambient, it interacts with the LC or the compounds such as 4-(4-dihexadecylsminostyryl)-N-meth functionalized Surface and the liquid crystal undergoes ylpyridinium iodide (DIA): 1,3,5,7,8-pentamethyl-2,6-di-t- phase transition, e.g., from the nematic to the isotropic butylpyrromethane-difluoreborate (PM-597): 4-(dicynaom 65 phase. This causes a rotation of the transition moment of the ethylene)-2-methyl-6-(4-dimethylamino styryl)-4H-pyran dye molecule parallel to the polarization direction of the (DCM); eurobium(III) thenoyltrifluoroacetonate trihydrate excitation beam. The dye molecules then absorb the incident US 9,575,037 B2 37 38 wavelength and emit light at different wavelength. Thus, by analyte. As used herein, a 'sub-responsive” amount, con probing a liquid crystal-dye mixture using polarized light centration, mass, etc. of an analyte is an amount, concen propagating perpendicularly to the cell Surface, the presence tration, mass, etc. of the analyte that reacts with the device of the analyte in the environment can be probed. The liquid but that does not cause a detectable response (e.g., signal) crystal assay device cell is fabricated as described above 5 from the device. Exposure to a Sub-responsive amount of an except that it is filled with a liquid crystal-dye mixture. For analyte thus “pushes” or “primes” the device to demonstrate the interrogation, the polarization can be integrated on the a response to a small amount of analyte. liquid crystal cell or can be probed by sending polarized IV Analytes light. The methods and devices of the present technology can be In still further embodiments, the fluorescent properties of 10 used to detect a variety of analytes in the gas phase. The quantum dots are utilized for detecting analytes. The present present technology is not limited to the detection of any technology is not limited to any particular mechanism of particular type of analyte. Exemplary analytes include, but action. Indeed, an understanding of the mechanism of action are not limited to, Sulfur compounds, nitrogen compounds, is not necessary to understand the present technology. Nev thiols, alcohols, acids, oxides, alkanes, alkenes, alkynes, and ertheless, Some semiconductor quantum dots (e.g., with 15 phosphates. nanometer size) emit visible light when exposed to UV The present technology finds use in the detection of radiation. Due to quantum confinement, the electron-hole variety of Sulfur compounds. In some embodiments, the pairs trapped at the Surface have a large band gap. Because Sulfur compounds are from a group that includes Sulfides, of this large band gap, these semiconductor quantum dots disulfides, sulfites or sulfates, including but not limited to absorb light in the UV region. The wavelength of light hydrogen sulfide, Chloromethyl trifluoromethyl sulfide, Eth emitted by these fluorescence particles depends on their size ylene sulfide, Dimethyl sulfide, Methyl Sulfide, Propylene and on properties of the Surrounding medium, Such as but sulfide, Trimethylene sulfide, 2-Chloroethyl methyl sulfide, not limited to, the dielectric constant of the Surrounding 2-(Methylthio)ethanol, Ethyl methyl sulfide, Bis(methylth medium. In some embodiments, these quantum dots are io)methane, 2-(Methylthio)ethylamine, N-Methyl-1-(meth functionalized with a receptor targeted for the analyte so that 25 ylthio)-2-nitroethenamine, Allyl methyl sulfide, 2-Chloro a liquid crystal in contact with them assumes an orientation ethyl ethyl sulfide, 3-(Methylthio)-1-propanol, 2,2'- perpendicular to the Surface of the quantum dots. Upon Thiodiethanol, 2,2'-Dithiodiethanol, Diethyl sulfide, Methyl irradiation from a UV light source, the fluorescent spectrum propyl disulfide, Tris(methylthio)methane, 2-(Ethylthio)eth shows a peak at a particular wavelength. When these dots are ylamine, 3-(Methylthio)propylamine, Cystamine dihydro exposed to the analyte, the liquid crystal undergoes a phase 30 chloride, 4-(Methylthio)-1-butanol, tert-Butyl methyl sul transition, which causes a shift in the peak position. fide, Cyclohexene sulfide, Diallyl sulfide, Allyl disulfide, The present technology is not limited to the use of any 3,3'-Thiodipropanol, 3,3'-Thiodipropanol, 3,6-Dithia-1.8- particular type of quantum dot. In some preferred embodi octanediol, Dipropyl sulfide, Isopropyl sulfide, Dipropyl ments, cadmium selenide quantum dots with thin Zinc sul disulfide, Isopropyl disulfide, 4-(Trifluoromethylthio)bro fide and polymer coatings are functionalized with a carbox 35 mobenzene, 4-(Trifluoromethylthio)phenol, Phenyl trifluo ylic acid terminated organic layer (for example romethyl sulfide, 3,5-Dichlorothioanisole, Chloromethyl 11-mercaptoundecanoic acid) and then treated to display a 4-chlorophenyl sulfide, 4-(Trifluoromethylthio)aniline, reactive moiety as described above (e.g., aniline-like 2-Bromothioanisole, 3-Bromothioanisole, 4-Bromothioani groups). In some preferred embodiments, the quantum dots sole, 2-Chlorothioanisole, 3-Chlorothioanisole, 4-Chloroth are dispersed in a liquid crystal (e.g., 5CB). The function 40 ioanisole, Chloromethyl phenyl sulfide, 2-Fluorothioanisole, alized quantum dots influence the phase of the liquid crystals 4-Fluorothioanisole, 4-Nitrothioanisole, Thioanisole, (nematic). In further preferred embodiments, a liquid crystal 2-(Methylthio)aniline, 3-(Methylthio)aniline, 4-(Methyl assay device is fabricated by forming a cavity (preferably 5 thio)aniline, 2-(Methylthio)cyclohexanone, 3-(Methylthio)- to 100 microns, most preferably about 25 microns) between 1-hexanol, 4-(Trifluoromethylthio)benzyl bromide, 4-(Trif two untreated UV transparent quartz substrates. The cavity 45 luoromethylthio)benzyl alcohol, Phenyl vinyl sulfide, between the substrates is filled with the mixture of func 4-(Methylthio)benzyl bromide, 2-Chloroethyl phenyl sul tionalized quantum dots and liquid crystal. In still further fide, 4-(Methylthio)benzyl chloride, 2-Methoxythioanisole, preferred embodiments, the optical cell is exposed to an 2-(Phenylthio)ethanol, 4-Methoxythioanisole, 4-(Methyl analyte (such as nitric oxide or nitrogen dioxide) and then thio)benzyl alcohol, Methoxymethyl phenyl sulfide, Ethyl probed with a UV light source, such as a laser. When the 50 phenyl sulfide, Methyl p-tolyl sulfide, Dibutyl sulfide, Dibu analyte binds to the receptors on the quantum dots, the liquid tyl disulfide, Bis(trimethylsilylmethyl) sulfide, Phenyl prop crystal undergoes a phase transition to isotropic, disrupting argyl Sulfide, (4-Chlorophenylthio)acetone, Benzyl 2.2.2- the quantum dots and thereby affecting the color of light trifluoroethyl sulfide, 4'-(Methylthio)acetophenone, Allyl emitted by them. phenyl sulfide, Cyclopropyl phenyl sulfide, 2-Nitro-5-(pro Electrical Detection 55 pylthio)aniline, S-Benzylcysteamine hydrochloride, Iso In some embodiments, a change in the physical properties amyl sulfide, 4-Methylthioisobutyrophenone, Pentafluoro of an LC is detected by measuring a change in the dielectric phenyl sulfide, Bithionol, Bis(3,5-dichlorophenyl) disulfide, constant of the liquid crystals that results from an interaction Bis(3,5-dichlorophenyl) disulfide, Bis(4-chlorophenyl) dis of the analyte with the LC. ulfide, 3-Nitrophenyl disulfide, 4-Nitrophenyl disulfide, Bis Sub-Responsive Exposure to Analyte 60 (2-nitrophenyl) disulfide, 2-Nitrophenyl phenyl sulfide, In some embodiments, devices are exposed to a “sub 4-Nitrophenyl phenyl sulfide, 2-(4-Chlorophenylthio)ani responsive” amount of an analyte prior to its use to detect the line, 4-Amino-4'-nitrodiphenyl sulfide, 3,3'-Dihydroxydi analyte (e.g., prior to exposing the device to a sample phenyl disulfide, Diphenyl sulfide, Diphenyl disulfide, Phe comprising or Suspected of comprising the analyte). In these nyl disulfide, 2-(Phenylthio)aniline, 2,2'- embodiments, the device will demonstrate a response to a 65 Diaminophenylsulfide, 4,4'-Diaminodiphenyl sulfide, 2,2'- lower amount of analyte in a test sample than a device that Dithiodianiline, Hexyl sulfide, Benzyl phenyl sulfide, Bis has not been exposed to a Sub-responsive amount of the (phenylthio)methane, Dodecyl methyl sulfide, 2-Nitro-p- US 9,575,037 B2 39 40 tolyl disulfide, Bis(4-methoxyphenyl) disulfide, Dibenzyl limited to methylamine, ethanolamine, trisamine, dimethyl sulfide, Dibenzyl disulfide, p-Tolyl disulfide, Benzyl trisul amine, methylethanolamine, aziridine, azetidine, pyrroli fide, 2-2-(Aminomethyl)phenylthiobenzyl alcohol, Pheny dine, piperidine, trimethylamine, dimethylethanolamine, lacetyl disulfide, Dioctyl sulfide, Chlorotriphenylmethyl dis aniline, cadaverine, idole, putrescine, and bis-tris methane. ulfide, Tris(phenylthio)methane, Tris(phenylthio)methane, In some embodiments, the gas compound is a thiol, Dodecyl sulfide, Hexakis(4-methylphenyl)thiobenzene, including but not limited to methanethiol, ethanethiol, cys and Hexakis(benzylthio)benzene, Potassium methyl sulfate, teine, 2-mercaptoethanol, dithiothreitol, and 2-mercaptoin Formaldehyde-sodium bisulfite adduct, Methyl sulfate dole. Sodium salt, Glyoxal bis(Sodium hydrogen Sulfite) adduct In some embodiments, the gas compound is an alcohol. hydrate, Ethylene sulfite, Glyoxal sodium bisulfite addition 10 The alcohol may be cyclic or acyclic, may be represented by compound hydrate, Dimethyl sulfite, Diethyl sulfite, Glut an organic compound that is a primary, secondary or tertiary araldehyde sodium bisulfite addition compound, Dipropyl alcohol including but not limited to methanol, ethanol, Sulfate, 4-Acetylphenyl Sulfate potassium salt, Sodium isopropanol, tert-butyl alcohol, propanol, cyclopropanols, 2-ethylhexyl sulfate, Sodium octyl sulfate, Dibutyl sulfate, cyclobutanols, cyclopentanols, cyclopropanols, cyclohexa 4-Hydroxy-3-methoxyphenylglycol sulfate potassium salt, 15 nol, cycloheptanols, benzylic alcohols, diarylmethanols, and Sodium dodecyl sulfate, Ammonium lauryl Sulfate solution, allylic alcohols. Tetradecyl sulfate sodium salt, and Octadecyl sulfate sodium In some embodiments, the gas compound is an acid. The salt. acid may be organic or inorganic, monoprotic, diprotic or In some embodiments the Sulfur compounds are from a triprotic, including but not limited to acetic acid, Sulfuric group that includes triflates such as but limited to (Trimeth acid, hydrochloric acid, hypochlorous acid, chorous acid, ylsilyl)methyl trifluoromethanesulfonate, (Trimethylsilyl) chloric acid, perchloric acid, hydrobromic acid, hydroiodic methyl trifluoromethanesulfonate, 4-Nitrophenyl trifluo acid, hydrofluoric acid, nitric acid, nitrous acid, carbonic romethanesulfonate, Phenyl trifluoromethanesulfonate, acid, phosphoric acid, citric acid, formic acid, chromic acid, 1-Cyclohexenyl trifluoromethanesulfonate, Catechol bis(tri methanesulfonic acid, ethanesulfonic acid, benzenesulfonic fluoromethanesulfonate), p-Tolyl trifluoromethanesulfonate, 25 acid, toluenesulfonic acid, folic acid, and salicylic acid. 4-Acetylphenyl trifluoromethanesulfonate, 2,6-Dimethoxy In some embodiments, the gas compound is an oxide or phenyl trifluoromethanesulfonate, 3,5-Dimethoxyphenyl tri its derivative, including but not limited to oxygen, nitric fluoromethanesulfonate, 2-(Trimethylsilyl)phenyl trifluo oxide, nitrous oxide, nitrogen dioxide, nitrogen dioxide, romethanesulfonate, Di-tert-butylsilyl bis carbon monoxide, carbon dioxide, Sulfur dioxide, oZone, and (trifluoromethanesulfonate), 1-Naphthyl 30 peroxides. trifluoromethanesulfonate, 2-Naphthyl trifluoromethanesul In some embodiments, the gas compounds are phosphates fonate, 4,4'-Biphenol bis(trifluoromethanesulfonate), 3.5- that may be organic or inorganic, including but not limited Di-tert-butylphenyl trifluoromethanesulfonate, 1,1'-Bi-2- to ammonium phosphate, boranophosphate, diammonium naphthol bis(trifluoromethanesulfonate). phosphate, phosphagen, phosphate, phosphoric acid, phos In some embodiments, the Sulfur is in an oxidized state, 35 photungstic acid, polyphosphate, pyrophosphoric acid, and including but not limited to sulfur dioxide, sulfur trioxide, urea phosphate. In some embodiments, the organophos sulfuric acid, sulfur oxide, Methyl phenyl sulfoxide, Phenyl phates are those used as pesticides, including, but not limited vinyl sulfoxide, Methyl p-tolyl sulfoxide, Butyl sulfoxide, to, Acephate (Orthene), AZinphos-ethyl, AZinphos-methyl Methyl 2-phenylsulfinylacetate, Diphenyl sulfoxide, p-Tolyl (Guthion), AZinphos-methyl oxon, Bromophos-methyl, Car sulfoxide, Dodecyl methyl sulfoxide, and Dibenzyl sulfox 40 bophenothion (Trithion), Chlorfenvinphos (Supona), Chlo ide. In other embodiments, the sulfur is in a compound with ropyrifos (Dursban/Lorsban), Chlorpyrifos-methyl, Chlo halogenated elements, such as Sulfenyl halides, sulfinyl rthiophos, Coumaphos (Co-Ral), Crotoxyphos (Ciodrin), halides, and sulfonyl halides including but not limited to Cyanophos, DEF (Butifos), Demeton (Systox), Demeton Chlorocarbonylsulfenyl chloride, Methoxycarbonylsulfenyl Dialifor (Torok), Diazinon (O Analog), Diazinon (Spec chloride, 2,4-Dinitrobenzenesulfenyl chloride, 4-Nitroben 45 tracide), Dichlorvos-DDVP (Vapona), Dicrotophos (Bidrin), Zenesulfenyl chloride, Trichloromethanesulfinyl chloride, Dimethoate (Cygon), Dioxathion (Delnav), Disulfoton (Di tert-Butylsulfinyl chloride, 2,4,5-Trichlorobenzenesulfonyl syston), Disulfoton Sulfone, Edifenphos, EPN, Ethion chloride, 3,4-Dichlorobenzylsulfonyl chloride, 2-Chlo (Nialate), Ethoprop (Mocap), Ethyl Parathion, Fenamiphos robenzylsulfonyl chloride, Trichloromethanesulfonyl chlo (Nemacur), Fenitrothion (Sumithion), Fensulfothion ride, Methanesulfonyl fluoride, Chlorosulfonylacetyl chlo 50 (Dasanit), Fenthion (Baytex), Fonofos (Dyfonate). Formo ride, N,N-Dimethylsulfamoyl chloride, thion, Heptenophos, Imidan (PhoSmet), Isazophos (Tri Cyclopropanesulfonyl chloride, 2-Propanesulfonyl chloride, umph), Isofenphos (Amaze), Leptophos (PhoSvel), Perfluoro-1-butanesulfonyl fluoride, 2-Bromo-4,6-difluo Malaoxon, Malathion (Celthion), Merphos (Tribufos), robenzenesulfonyl chloride, 2,3,4-Trichlorobenzenesulfonyl Methamidophos (Monitor 4), Methidathion, Methyl Para chloride, 2,5-Dibromobenzenesulfonyl chloride, Benzene-1, 55 thion (Metacide), Mevinphos (Phosdrin), Monocrotophos, 3-disulfonyl chloride, Cyclohexanesulfonyl chloride, Naled, Omethoate (Dimethoate O analog), Parathion (Alk m-Toluenesulfonyl chloride, disulfur dichloride, sulfur ron), Paroxon, Phorate (Thimet), Phorate-o, Phorate Sul hexafluoride, thionyl chloride, and sulfuryl chloride. fone, Phorate Sulfoxide, Phosalone, Phosphamidon (Dime In some embodiments, the gas compound contains nitro cron), Piperophos, Pirimiphos-ethyl, Pirimiphos-methyl, gen, including but not limited to nitrogen, ammonia, 1.3.5- 60 Profenofos (Curacron), Propetamphos (Safrotin), Pyrazo Trinitrobenzene(TNB), Methyl nitrate, Nitroglycerin (NG), phos (Afgan), Quinalphos, Ronnel (Ectoral) (Fenchlorphos), Triaminotrinitrobenzene (TATB), and Pentaerythritol tet Sulprofos (Bolstar), Terbufos (Counter), Tetrachlorvinphos ranitrate (PETN). In some embodiments, the nitrogen con (Gardona). Thionazin (Zinophos), and TriaZophos (Hosta taining compound is an amine. The amine may have an alkyl thion). In some embodiments, the organophosphates are or an aryl functional group, may be aliphatic or aromatic in 65 nerve agents (e.g., agents of war), including, but not limited structure, may be represented by an organic compound that to G agents (GD, Soman: GB, Sarin; and GA, tabun) and the is a primary, secondary or tertiary amine including but not V agents (VX). US 9,575,037 B2 41 42 In some embodiments, the analyte comprises an alkane VI Substrates (e.g., a paraffin), e.g., an alkane comprising between 4 and Substrates that find use in practicing the present technol 12 carbon atoms per molecule (commonly referred to as ogy can be made of practically any physicochemically stable C4-C12, e.g., butane, pentane, hexane, heptane, octane, material. In a preferred embodiment, the substrate material nonane, decane, undecane, dodecane). In some embodi is non-reactive towards the constituents of the mesogenic ments, the analyte comprises an n-alkane and in some layer. The substrates can be either rigid or flexible and can embodiments, the analytes comprises a branched alkane. In be either optically transparent or optically opaque. The Some embodiments, the analyte comprises a cycloalkane Substrates can be electrical insulators, conductors or semi and/or a naphthene. In some embodiments, the analytes conductors. Further, the substrates can be substantially comprises an alkene (e.g., olefin), cycloalkene, isoalkane, 10 aromatic (e.g., benzene, toluene, Xylene, ethylbenzene, impermeable to liquids, vapors and/or gases or, alternatively, C3-benzene, C4-benzene), and/or an alkyne. the substrates can be permeable to one or more of these In some embodiments, the analyte comprises a mixture of classes of materials. Exemplary Substrate materials include, organic compounds that is known by the general name of but are not limited to, inorganic crystals, inorganic glasses, “gasoline”, “petrol”, “casing head gasoline”, “motor fuel”, 15 organic glasses, inorganic oxides, metals, metal oxides, or “motor spirit'. Accordingly, in Some embodiments, the semiconductors, conductors, salts, organic polymers and analytes is or comprises an additive and/or blending agent combinations thereof. In some embodiments, the Substrates Such as an anti-knock agent, anti-oxidant, metal deactivator, have micropillared features thereon for the stabilization of lead Scavenger, anti-rust agent, anti-icing agent, upper the liquid crystal overlay and/or other reagents to the Sub cylinder lubricant, detergent, and/or a dye. strate surface or detection regions thereon. V Reactive Moieties Inorganic Crystal and Glasses A wide variety of chemical sensors can be fabricated that In some embodiments of the present technology, inor will detect trace chemical vapors utilizing the interactions ganic crystals and inorganic glasses are utilized as Substrate between liquid crystals and the analyte. The physical (e.g., materials (e.g., LiF, NaF. NaCl, KBr, KI, CaF, MgF. HgF. optical and electrical) and the alignment properties of liquid 25 BN, AsS., ZnS, SiNa, and the like). The crystals and glasses crystal are governed by the intermolecular interactions of its can be prepared by conventional techniques (see, e.g., functional moieties where a chemical change in the liquid Goodman. Crystal Growth. Theory and Techniques, Plenum crystal moiety is likely to alter its properties. Liquid crystal Press, New York 1974). Alternatively, the crystals can be has the ability to influence the rates and energetics of organic purchased commercially (e.g., Fisher Scientific). The crys reactions due to its integrated molecular arrangements. 30 Incorporating a functional moiety that reacts with the target tals can be the Sole component of the Substrate or they can analyte can affect a change in liquid crystal molecules that be coated with one or more additional Substrate components. will be translated into its observed properties. Thus, it is within the scope of the present technology to The present technology provides a method for the detec utilize crystals coated with, for example, an organic poly tion or differentiation and quantitative measurement of a 35 mer. Additionally, a crystal can constitute a portion of a wide range of chemical vapors, such as oxides of nitrogen, Substrate that contacts another portion of the Substrate made oZone, amines, alcohols, thiols, etc. The liquid crystal can be of a different material, or a different physical form (e.g., a tuned or functionalized by a combination of processes. Such glass) of the same material. Other useful Substrate configu as, liquid crystals having reactive organic functional groups rations utilizing inorganic crystals and/or glasses will be (-OH, C—C , C=C N-N , NH2, 40 apparent to those of skill in the art. —COOH, etc.), metal-ligand interaction, metal-liquid crys Inorganic Oxides tal interaction, metal-ligand-liquid crystal interaction. The In other embodiments of the present technology, inorganic choice of a particular liquid crystal composition will be oxides are utilized as the Substrate. Inorganic oxides of use based on the analyte that interacts with LC either by chemi in the present technology include, for example, CSO. cal reaction, metal-ligand coordination interaction, or 45 Mg(OH), TiO, ZrO, CeO YO. Cr-O, Fe2O, NiO, dipole-dipole interactions (e.g., by changes in the polarity of ZnO, Al2O, SiO (glass), quartz. In O, SO, PbO2, and the the LC environment) that fulfills the requirements: (i) the like. The inorganic oxides can be utilized in a variety of target vapors should interact strongly with the LC, and (ii) physical forms such as films, Supported powders, glasses, this interaction must be coupled to a change in the LC. crystals, and the like. A Substrate can consist of a single The interaction between the analyte and the LC will be 50 inorganic oxide or a composite of more than one inorganic dependent on the analyte of interest and the active functional oxide. For example, a composite of inorganic oxides can group present in the LC. This particular detection mecha have a layered structure (e.g., a second oxide deposited on nism will involve acid-base, oxidation-reduction, Substitu a first oxide) or two or more oxides can be arranged in a tion reaction, or combinations thereof at the functionalized contiguous non-layered structure. In addition, one or more moiety in the liquid crystal. The interaction of the target 55 oxides can be admixed as particles of various sizes and analytes with the liquid crystals will manifest as a change in deposited on a Support such as a glass or metal sheet. the physical properties of liquid crystals (phase transition, Further, a layer of one or more inorganic oxides can be optical birefringence, dielectric anisotropy, magnetic isot intercalated between two other Substrate layers (e.g., metal ropy, or change in the orientation of liquid crystals on a oxide metal, metal oxide-crystal). Surface) that can be detected using a variety of instruments 60 In some embodiments, the Substrate is a rigid structure capable of detecting these physical changes. that is impermeable to liquids and gases. In this embodi A variety of reactive moieties find use in the present ment, the Substrate consists of a glass plate onto which a technology. In some embodiments, the reactive moieties are metal. Such as gold, is layered by evaporative deposition. In functional groups available on the liquid crystal that is a still further embodiment, the Substrate is a glass plate overlaid on a Substrate. In some embodiments, a Substrate is 65 (SiO2) onto which a first metal layer Such as titanium or gold overlaid with a thin film of a solution to provide the reactive has been layered. A layer of a second metal (e.g., gold) is groups on the Surfaces of the Substrate. then layered on top of the first metal layer (e.g., titanium). US 9,575,037 B2 43 44 Organic Polymers and Glasses Micro-Structured Features In still other embodiments of the present technology, In some embodiments, the substrates utilized in the organic polymers are utilized as Substrate materials. Organic devices of the present technology comprise one more micro polymers useful as Substrates in the present technology structured features. In some embodiments, micro-structured 5 features on the Substrate augment the spreading of the liquid include polymers that are permeable to gases, liquids, and crystal composition. In still other embodiments, the micro molecules in solution. Other useful polymers are those that structured features stabilize the liquid crystal overlay and/or are impermeable to one or more of these same classes of other reagents on the Substrate surface or detection regions compounds. Many of these polymers can be prepared as thereon. In a paper by Frisk et al (2006, Lab on a Chip 6: glasses. 1504), liquid was dispensed onto a micromachined biosen Organic polymers that form useful substrates include, for 10 sor Substrate that was Suspended vertically and remained example, polyalkenes (e.g., polyethylene, polyisobutene, stably dispersed (and immune to gravitational forces and polybutadiene), polyacrylics (e.g., polyacrylate, polymethyl shock) on that substrate. Following on this result, Sridhara methacrylate, polycyanoacrylate), polyvinyls (e.g., polyvi murthy et al (2008, Smart Mater Struct 17) demonstrated nyl alcohol, polyvinyl acetate, polyvinyl butyral, polyvinyl that microstructures could be used to Support a film of liquid chloride), polystyrenes, polycarbonates, polyesters, polyure 15 crystal. In contrast to these systems, in some preferred embodiments, the micro-structured features are made my thanes, polyamides, polyimides, polysulfone, polysiloxanes, depositing a polymer on the Substrate and etching away polyheterocycles, cellulose derivatives (e.g., methyl cellu areas between the micro-structured features or made from lose, cellulose acetate, nitrocellulose), polysilanes, fluori the same material as the Substrate. Additionally, in some nated polymers, epoxies, polyethers, and phenolic resins embodiments, the analyte interacts and/or reacts with the LC (see, Cognard (1982) “Alignment of Nematic Liquid Crys composition rather than competing at the Surface of the tals and Their Mixtures” in Mol. Cryst. Liq. Cryst. 1: 174). substrate. Some organic polymers include polydimethylsiloxane, poly Accordingly, in some embodiments, the micro-features ethylene, polyacrylonitrile, cellulosic materials, polycarbon pattern the Surface and are selected from the group consist ates, and polyvinyl pyridinium. 25 ing of a grid, a channel, a plurality of pillars, or an array of In some embodiments, the Substrate is permeable and it assay areas, or combination thereof. In some embodiments, comprises a layer of gold, or gold over titanium, which is the micro-features are pillars that project from the surface of deposited on a polymeric membrane, or other material, that the Substrates. In some embodiments, the Substrates are is permeable to liquids, vapors, and/or gases. The liquids and comprised of glass, silicon, polymer, or a combination gases can be pure compounds (e.g., chloroform, carbon 30 thereof. In still further embodiments, the pillars are com prised of the same material as the surface. In other embodi monoxide) or they can be compounds that are dispersed in ments, the pillars are comprised of a different material than other molecules (e.g., aqueous protein solutions, herbicides the Surface. In some embodiments, the Substrate is glass in air, alcoholic solutions of Small organic molecules, etc.). while the pillars are made from a polymeric material. The Useful permeable membranes include, but are not limited to, 35 pillars may comprise a shape selected from the group flexible cellulosic materials (e.g., regenerated cellulose consisting of circular, triangular, Square, hexagonal, or a dialysis membranes), rigid cellulosic materials (e.g., cellu combination thereof. The dimension of the pillars could be lose ester dialysis membranes), rigid polyvinylidene fluoride a variety of heights, widths, and spacings. Indeed, the pillar membranes, polydimethylsiloxane, and track etched poly height may range from 1 micron to 50 microns, the width carbonate membranes. 40 from 1 micron to 200 microns, and the spacing between In a further embodiment, a layer of gold on the permeable pillars may range from 1 micron to 200 microns. membrane is itself permeable. In some embodiments, the VII Mesogens permeable gold layer has a thickness of about 70 Angstroms Any compound or mixture of compounds that forms a or less. mesogenic layer can be used in conjunction with the present In those embodiments wherein the permeability of the 45 technology. The mesogens can form thermotropic, lyotropic, Substrate is not a concern and a layer of a metal film is used, metallotropic, or cholesteric liquid crystals. The thermo the film can be as thick as is necessary for a particular tropic, lyotropic, metallotropic, and cholesteric liquid crys application. For example, if the film is used as an electrode, tals can exist in a number of forms including nematic, the film can be thicker than in an embodiment in which it is isotropic, chiral nematic, Smectic, polar Smectic, chiral necessary for the film to be transparent or semi-transparent 50 Smectic, frustrated phases, and discotic phases. to light. Some mesogens that find use in embodiments of the Thus, in Some embodiments, the film has a thickness from technology are displayed in Table 2. In some embodiments, about 0.01 nanometer to about 1 micrometer, e.g., about 5 the mesogen is 5CB (4-pentyl-4'-cyanobiphenyl), MLC nanometers to about 100 nanometers. In some embodiments, 6812, MLC 12200, MBBA, EBBA, or 8CB (4-cyano-4'- the film has a thickness of from about 10 nanometers to 55 octylbiphenyl), and combinations thereof. about 50 nanometers. The mesogenic layer can be a Substantially pure com Arrays pound, or it can contain other compounds, so called dopants, In some embodiments, the LC composition comprising that enhance or alter characteristics of the mesogen. Thus, in reactive moieties is arrayed on the Substrates using stamp Some embodiments, the mesogenic layer further comprises ing, microcontact printing, or ink-jet printing. In still further 60 a second compound, for example an alkane, which expands embodiments, reactive moieties are spotted onto a suitable the temperature range over which the nematic and isotropic Substrate. Such spotting can be done by hand with a capillary phases exist. Use of devices having mesogenic layers of this tube or a micropipette, or by an automated spotting appa composition allows for detection of the analyte reactive ratus such as those available from Affymetrix and Gilson moiety interaction over a greater temperature range. (see, e.g., U.S. Pat. Nos. 5,601,980; 6.242.266; 6,040, 193; 65 In some embodiments, the mesogenic layer further com and 5,700,637; each of which is incorporated herein by prises a dichroic dye or a fluorescent compound. Examples reference). of dichroic dyes and fluorescent compounds useful in the US 9,575,037 B2 45 46 present technology include, but are not limited to, azoben the absorbance of the liquid crystal is in the visible range, Zene, BTBP polyazo compounds, anthraquinone, perylene then phase changes can be observed using ambient light dyes, and the like. In some embodiments, a dichroic dye of without crossed polarizers. In some embodiments, the a fluorescent compound is selected that complements the dichroic dye or fluorescent compound is used in combina orientation dependence of the liquid crystal so that polarized 5 tion with a fluorimeter and changes in fluorescence are used light is not required for the assay. In some embodiments, if to detect changes in phase transition of the liquid crystal. TABLE 2

Molecular structures of mesogens suitable for use in embodiments of liquid crystal assav devices

Mesogen Structure

Anisaldazine co-o-O-ch-s-s-ch O-CH NCB call-O-O-O. CBOOA cal-o-O)-s-ch-O-G Comp A call-O-O-to-O)-se Comp B DBNO, call-O-o-o-O-o-o-O)-so DOBAMBC CH3 M CoH-O CHEN CH=CH-COO-CH-CH V CH5

nOm n = 1, m = 4: MBBA n = 2, m = 4: EBBA CH-O ci--O-cal nOBA n = 8: OOBA n = 9: NOBA CnH2n+ -o-O)-cool nmOBC cal-o-o-O-O-o-cal nOCB

nOSI CH-O COO CH-CH

N US 9,575,037 B2 47 48 TABLE 2-continued

Molecular structures of mesogens Suitable for use in embodiments of liquid crystal assav devices Mesogen Structure

PAA CH-O NEN O-CH V / O

PYP906 N

cut-O-O-o-calN nSm CH-O CO-S CnH2n+1

Although the disclosure herein refers to certain illustrated 20 treatment, then rinsed thoroughly with ethanol and dried in embodiments, it is to be understood that these embodiments a stream of N. The slides were cut into three 1"x1" pieces are presented by way of example and not by way of and two pieces were spin coated with 1 ml of a 2 mM limitation. ethanolic solution of lead (II) perchlorate. The other piece was coated with 1 mM lead (II) perchlorate. After spin EXAMPLES 25 coating, the pieces were cut in half (1"x0.5") to provide substrates for three sandwich cells. The sandwich cells were The following examples are provided to demonstrate and fabricated by pairing a substrate with another identically further illustrate certain embodiments and aspects of the present technology and are not to be construed as limiting treated substrate. To access the effect of thickness of the the scope thereof. 30 sandwich cell, one 25 micron and one 50 micron thick cell In the experimental disclosure that follows, the following were fabricated from 2 mM coated substrate while one 25 abbreviations are used: eq. (equivalents); M (molar): LM micron cell was fabricated from 1 mM coated Substrate. Two (micromolar); N (Normal); mol (moles); mmol (millimoles): Substrates, with the functionalized surfaces facing each umol (micromoles); nmol (nanomoles); g (grams); mg (mil other, were separated by mylar spacers with desired thick ligrams); Lug (micrograms); ng (nanograms); 1 or L (liters); 35 ness (e.g. 25 or 15 micron) by placing one long mylar piece ml (milliliters); ul (microliters); cm (centimeters); mm (mil along one of the short ends and two small pieces at two limeters); um (micrometers); nm (nanometers); C (degrees corners of the other short end. The two pieces were held Centigrade); U (units), mu (milliunits); min. (minutes); sec. together by using binder clips. Each sandwich cell was filled (seconds). with 10 ul of LC E7, by capillary action through space 40 between the small mylar pieces. Example 1 Microfluidic cell with large single sensing area "(long sensor) was also prepared using 3.8 cm x 1.9 cm glass Comparison Between Microfluidic Cells and Substrate coated with polymer micropillars fabricated using Sandwich Cells standard photolithography. The polymer micropillars were 5 45 micron tall, 10 micron diameter with 20 micron center-to During the development of embodiments of the technol center spacing and covered 3.5 cmx1.3 cm area on the glass ogy provided herein, data were collected from testing tra substrate. The micropillared glass substrate was coated with ditional sandwich cells (LC cells where all the space 20A thick titanium layer followed by 100 A thick gold film. between two surfaces was filled with LC), microfluidic cells The gold coated substrates were chemically functionalized with Small discrete sensing areas (i.e. LC cells with a 50 by forming self-assembled monolayer of 11-mercaptound headspace between a Substrate with discrete sensing areas ecanoic acid (MUA) after incubating the substrate in 1 mM and top surface) and microfluidic cells with large single ethanolic solution for ~16 hrs. These substrates were then sensing area (i.e. LC cells with a headspace between a rinsed thoroughly with ethanol and dried in a stream of N. Substrate with large sensing areas and top surface). Some The substrates were then briefly (15 s) subjected to UV experiments were also performed with varying thicknesses 55 oZone treatment, then rinsed thoroughly with ethanol and of LC between the two sides of the sandwich cell and also dried in a stream of N. The microstructured substrate was varying thicknesses of the head space in microfluidic cells to then spin coated with 1 mL of 2 mMethanolic solution of access the effect of thickness in the response. lead(II) perchlorate and spotted with 4 ul of a 20/30.3 A traditional sandwich LC cell was prepared first by mixture of E7 and octane. The resultant substrate was paired coating a 1"x3"aluminosilicate (AlSi) glass slide with 20 A 60 with OTS treated substrates forming a head space above the thick titanium layer followed by 100 A thick gold film. The LC film using 12 micron (sensor 1), 15 micron (Sensor 2) gold coated slides were chemically functionalized by form top, 25 micron (sensor 3), and 50 micron (Sensor 4) thick ing self-assembled monolayer of 11-mercaptoundecanoic mylar strips. acid (MUA) after incubating the slide in 1 mM ethanolic Microfluidic cells with 10 discrete sensing areas in 2 rows solution for ~16 hrs. These slides were then rinsed thor- 65 “2x5 sensors” were fabricated by using a 2x5 array of oughly with ethanol and dried in a stream of nitrogen (N). micropillared area (~5 mm across) spaced ~8.5 mm (center The slides were then briefly (15 s) subjected to UV ozone to-center) apart on an ~43 mmx17 mm glass Substrates. The US 9,575,037 B2 49 50 polymer micro pillars on the glass Substrate were fabricated ments of liquid cells to detect an analyte (e.g., HO. For using standard wet photolithography and were 5 micron tall, example, in Some experiments, traditional sandwich cells 10 micron diameter and are spaced by 20 micron (center (cells with all the space between two substrate filled with to-center). The micropillared substrates were coated with 20 LC) were constructed and their performance to detect HS A thick titanium layer followed by 100A gold film. The gold 5 was compared with microfluidic cells (cells with a head coated slides were chemically functionalized by forming self space between the top surface and LC film) fabricated using assembled monolayer of 11-mercaptoundecanoic acid identical protocol. (MUA) after incubating the substrate in 1 mM ethanolic solution for ~16 hrs. These substrates were then rinsed A traditional sandwich LC cell was prepared first by thoroughly with ethanol and dried in a stream of nitrogen coating a 1"x3"aluminosilicate (AlSi) glass slide with 20 A (N). The slides were then briefly (15 s) subjected to UV 10 thick titanium layer followed by 100 A thick gold film. The oZone treatment, then rinsed thoroughly with ethanol and gold coated slides were chemically functionalized by form dried in a stream of N. The substrate was then spin coated ing self-assembled monolayer of 11-mercaptoundecanoic with 2 mM lead(II) perchlorate. The micropillared areas (5 acid (MUA) after incubating the slide in 1 mM ethanolic mm across) were then spotted two times with 0.14 ul of an solution for ~16 hrs. These slides were then rinsed thor E7-octane mixture (25%-7.5%). The LC filled sensor sub 15 oughly with ethanol and dried in a stream of nitrogen (N). strate was then paired with another glass Substrate coated The slides were then briefly subjected (15 s) to UV ozone with (Tridecafluoro-1,1,2,2-tetrahydrooctyl)-trichlorosilane treatment, then rinsed thoroughly with ethanol and dried in (OTS) with the functionalized surfaces facing each other. a stream of N. The slides were cut into three 1"x1" pieces Two mylar strips (12 micron thick) were placed along the and each piece was spin coated with 1 ml of a 4 mM long edge of the substrate to define the head space above the ethanolic solution of lead perchlorate. After spin coating, the LC film and the substrates were held together using binder pieces were cut in half (1"x0.5") to provide substrates for six clips. In a second 2x5 sensor, another mylar strip was placed sandwich cells. The sandwich cells were fabricated by along the middle to form a “channel’ separating the descrete pairing these substrates with (Tridecafluoro-1,1,2,2-tetrahy circular areas. drooctyl)-trichlorosilane (OTS) treated glass substrates with The 2x5 sensor, Sandwich cells, and long sensors were 25 similar dimensions. Two substrates, with the functionalized stored in the argon filled bag at 4° C. and exposed the Surfaces facing each other, were separated by mylar spacers following day to 1 ppm HS. Prior to opening the bag, all the cells were allowed to equilibrate to room temperature for 30 with desired thickness (e.g. 25 micron) by placing one long minutes. After equilibration, images of 2x5 sensors (FIG. 1 mylar piece along one of the short ends and two small pieces A), long sensors (FIG. 1 B), and sandwich cells (FIG. 1 C) at two corners of the other short end. The two pieces were were taken before exposure to 1 ppm HS for eight hours 30 held together by using binder clips. Each sandwich cell was (FIG. 1). The HS test chamber (21 Lit volume) was filled with 10 ul of LC E7, by capillary action through space equilibrated to 1 ppm HS at a flow rate of 4 L/min. for 15 between the small mylar pieces. minutes, then the sensors were placed inside, and the test A microfluidic cell was prepared using 3.8 cmx1.9 cm chamber was equilibrated for an additional 15 minutes at the glass Substrate coated with polymer micropillars fabricated same flow rate. The flow was then decreased to 1 L/min. and 35 using standard photolithography. The polymer micropillars all sensors were exposed at this rate for the remainder of 8 were 5 micron tall, 10 micron diameter with 20 micron hours. center-to-center spacing and covered 3.5 cmx1.3 cm area on After exposure to 1 ppm HS for eight hours images were the glass Substrate. The micropillared glass Substrate was acquired (FIG. 2). The 2x5 sensors show responses on the coated with 20 A thick titanium layer followed by 100 A first circles on both sides and the response is not affected by 40 thick gold film. The gold coated substrates were chemically the presence of an additional piece of mylar in the center of functionalized by forming self-assembled monolayer of the cell (FIG. 2A). The long sensors demonstrated a good 11-mercaptoundecanoic acid (MUA) after incubating the response, especially with 25 micron and 50 micron mylar substrate in 1 mM ethanolic solution for ~16 hrs. These (FIG. 2B). Thicker mylar produced brighter reacted areas substrates were then rinsed thoroughly with ethanol and and greater responses. The sandwich cells also gave a very 45 dried in a stream of N. The substrates were then briefly (15 small responses (FIG. 2C). s) subjected to UV ozone treatment, then rinsed thoroughly Long Sensor 3 was imaged 2 to 3 days after exposure to with ethanol and dried in a stream of N. The microstruc H2S and the image of the sensor was acquired. The appear tured substrate was then spin coated with 1 mL of 1 mL ance of the sensor was compared with that on the first day. ethanolic solution of lead(II) perchlorate. The micropillared The response of the sensor was stable (FIG. 2, compare with 50 area of the substrate was then filled with ~3 microliter of LC FIG. 2B, Sensor 3). E7: octane (40:60) mixture. After evaporation of the organic The results from this experiment show that (i) the micro solvent, the LC-filled substrate was then paired with an OTS fluidic cells (long sensor or 2x5 sensor) with head space are treated glass Substrate forming a head-space (e.g., a head more sensitive than the traditional sandwich cells fabricated space of approximately 20 microns), by placing two strips from identically prepared substrate (ii) the 15 micron spac 55 along the long side of the Substrate, to allow controlled ers provide for a small response and thicker spacers (e.g., 25 diffusion of the targeted analytes above the LC film. micron mylar) provide a greater response and (iii) relatively Once these sandwich cells were fabricated, the LC did not long cells (similar to 2x5 sensors) are appropriate for higher exhibit homeotropic alignment on these substrates while the concentrations of HS. microfluidic cells exhibited homeotropic alignment as 60 expected on lead (II) perchlorate treated substrates. These Example 2 results suggested that a format using a micropillared Sub strate may provide a better alignment of the LC on an Comparison Between Sensitivity of Sandwich Cells identically functionalized surface for analyte detection. As a and Microfluidic Cells result, experiments were conducted to compare performance 65 of microfluidic cell with headspace and sandwich cell fab During the development of embodiments of the technol ricated using slightly different preparation protocols. The ogy, experiments were conducted to develop new embodi sandwich cells were fabricated as described above except US 9,575,037 B2 51 52 the MUA functionalized surfaces were not treated with UV titanium layer followed by a 100 A thick gold film. The gold ozone as described above while the microfluidic cells were coated substrates were chemically functionalized by form fabricated as described above. This process produced sand ing a self-assembled monolayer of 11-mercaptoundecanoic wich cells with good initial LC alignment. acid (MUA) after incubating the substrate in 1 mMethanolic Experiments were performed by manufacturing six sand solution for ~16 hrs. These substrates were then rinsed wich cells and exposing them alongside six microfluidic thoroughly with ethanol and dried in a stream of N. The cells (e.g., prepared as described above) to compare substrates were then briefly (15 s) subjected to UV ozone responses. The sensors were manufactured and stored at 4 treatment, then rinsed thoroughly with ethanol and dried in C. until the experiment was performed. Two microfluidic a stream of N. The microstructured substrate was then spin cells and two sandwich cells were assigned to be exposed to 10 coated with 1 mL of ethanolic solution of lead(II) perchlo air at 45% RH (negative controls) and an additional four rate. The micropillared area of the substrate was then filled microfluidic cells and four Sandwich cells were assigned to with ~3 microliter of LC E7:octane mixture at 40:60 ratio. be exposed to 8 ppm HS at 45% RH for eight hours. After evaporation of the organic solvent, the LC-filled On the day of the exposure, microfluidic cells and sand substrate was then paired with an OTS treated glass sub wich cells were allowed to equilibrate at room temperature 15 strate forming a head-space (e.g., a head space of approxi for 15 minutes before opening the bags. Images were taken mately 20 microns) by placing a U-shaped mylar strip before the microfluidic and sandwich cells were exposed to around edge of the substrate, to allow controlled diffusion of H2S and of sensors assigned as negative (i.e. exposed to 45% the targeted analytes above the LC film. The substrates were Zero air) controls (FIG. 4 and FIG. 5). Before exposure, the held together using binder clips and three sides with the sandwich cells appeared homeotropic with the exception of mylar strips were sealed using low off-gassing epoxy to one bright spot in one of the cells assigned as negative force the gas diffusion through the open end of the sensor. control cells (FIG. 4) and one of the microfluidic cells (FIG. These cumulative sensors, fabricated in a lot of five, were 5). They were then placed in a large (-21 L) test chamber stored in an argon environment prior to use. and the HS flow inside the chamber was maintained at 5.8 Cumulative sensors were exposed inside a large (21 liter) liter/min for initial 15 minutes. After the cells had been in the 25 exposure chamber to 8 combinations of H2S concentration test chamber for 15 minutes at a 5.8 liter/minute flow rate, and time at 22°C. and 45% RH to determine the relationship the flow rate was decreased to 1.2 liter/minute for the between sensor response and H2S dose (concentrationX remainder of the eight-hour exposure. time). Sensors were also exposed to HS free air at 22°C. All of the microfluidic cells and sandwich cells were and 45% RH as a control. Four sensors were tested per dose. exposed together to either HS or Zero air (FIG. 6 and FIG. 30 An in-house gas delivery and testing apparatus that is 7). There are small responses that can be seen along the edge capable to generate HS concentrations from low ppb to 100 of the sandwich cells. The responses are barely visible after ppm was used to test the sensors. The exposure system also the eight hour exposure (FIG. 6 A). The sandwich cells allows generation of desired concentrations at desired tem exposed to Zero air show no responses after the eight hour peratures and humidity. For each test point 5 sensors were exposure (FIG. 6 B). The microfluidic cells show responses 35 made as described above; 1 sensor was exposed to 16 of birefringent fronts ranging from 17.4 to 20.4 mm (FIG. 7 ppm-hours at room temperature and 45% RH as a reference A). The microfluidic cells that were exposed to zero air show exposure for quality control and the other 4 sensors were no responses after the eight hour exposure (FIG. 7B). exposed to the test dose. Neither the microfluidic nor the sandwich cells showed any Additional experiments tested a microfluidic cell for response to Zero air at 45% RH. 40 measuring HS that was prepared as described in Example These results establish that the microfluidic cells (i) 1. provide more stable alignment of LC on similarly function Quality Verification and Test Procedure alized surface and (ii) are more sensitive to the target analyte On the day of exposure, the package of five sensors was (HS) compared to traditional sandwich cells. first allowed to equilibrate at room temperature for 15 45 minutes. After equilibration, one sensor was used as a QC Example 3 sensor. For each lot, a QC sensor was exposed to 8 ppm H2S at 45% RH for 2 hours (nominal dose of 16 ppm-hr). The Microfluidic Cell as a Cumulative Dosimeter HS test chamber (21 liter volume) was equilibrated at a flow rate of 5.8 L/minutes for 15 minutes before exposure; During the development of embodiments of the technol 50 the sensor was imaged, and then placed inside the test ogy provided herein, experiments were conducted to estab chamber. The test chambers were equilibrated for an addi lish that the microfluidic cells could be used as cumulative tional 15 minutes at the 5.8 liter/minute flow rate. The flow dosimeter by determining the relationship between response was then decreased to 1.2 liter/minute and the sensor was from these microfluidic cells “(cumulative sensors)” and exposed at this rate for the remainder of the 2 hours and 5 analyte dose. Experiments were conducted using a cumula 55 minutes. The sensor was again imaged after exposure. Then tive analyte sensor in an average environmental condition of the sensor was left at ambient temperature for 6 hours and 22° C. and 45% relative humidity (RH). imaged again to check for any change in response. In Cumulative Sensor Fabrication parallel, the remaining four sensors were exposed to the Cumulative sensors were designed to measure a total dose desired test concentrations for specified time inside another of gaseous H2S in a sample by integrating over the concen 60 identical exposure chamber following similar procedure. tration and exposure time. Cumulative sensors were pre Measurement of Response pared using 3.8 cmx1.9 cm glass Substrates coated with After exposure to the QC dose or the desired dose, digital polymer micropillars fabricated using standard photolithog images of the sensors were acquired using a digital scanner raphy. The polymer micropillars were 5 micron tall, 10 interfaced with a laptop. During the development of embodi micron diameter with 20 micron center-to-center spacing 65 ments of the technology provided herein, several different and covered 3.5 cm x 1.3 cm area on the glass substrate. The methods were evaluated for determining sensor response to micropillared glass substrate was coated with a 20 A thick analyte by analyzing images of exposed sensors. While the US 9,575,037 B2 53 54 technology is not limited in the methods that are appropriate concentrations of 15 ppb. 16.67 ppb. 25 ppb, and 50 ppb at for quantification of images, Image.J (NIH) was used in some exposure times of 72 hours, 72 hours, 48 hours, and 24 trials for analyzing sensor images acquired from a scanner. hours, respectively. Using the Image freeware, a simple method to calculate the These results indicate that much lower concentrations of width of the bright front (i.e. the distance the bright front has target gases are detectable by increasing the exposure time. traveled in an otherwise dark background) was developed. Such performance is of value for environmental monitoring Using this method, the response length was measured for where lower concentrations of toxic gas may be present for both the QC sensor and the sensors exposed to different extended times. doses. Results 10 Example 4 Images acquired of sensors exposed to 0, 0.8, 4, 8, 25, 40, 80, 120, and 160 ppm-hours of HS are provided in FIG. 8A through 8I. FIG. 8J shows an image acquired for the quality Effect of Head Space Height of the Microfluidic control experiment in which a sensor was exposed to 16 Cells on Sensitivity ppm-hours of H2S. 15 The average widths of the response fronts were deter During the development of embodiments of the present mined using Image.J and are plotted in FIG.9. The consistent technology, experiments were performed to determine the curve demonstrates that the sensors do provide a response to effect of head space height on the sensitivity of the micro total HS dose and are not skewed by shifting time and fluidic cells (“cumulative sensors”). concentration combinations. The relationship between Cumulative sensors were prepared using 3.8 cmx1.9 cm response length and dose resembles a square root curve. glass Substrates coated with polymer micropillars fabricated Plotting response length versus the square root of dose using standard photolithography. The polymer micropillars produces a linear relationship (FIG. 10). Without being were 5 micron tall, 10 micron diameter with 20 micron bound by theory, the square root relationship most likely center to center spacing and covered 3.5 cmx1.3 cm area on results from this being a process governed by laws of 25 the glass Substrate. The micropillared glass Substrate was diffusion of gas. coated with a 20 A thick titanium layer followed by a 100 After the dose response curve was generated, a verifica A thick gold film. The gold coated substrates were chemi tion test was performed by making four lots of sensors cally functionalized by forming self-assembled monolayers following the same protocol and exposing them to different of 11-mercaptoundecanoic acid (MUA) after incubating the concentrations. FIG. 10 shows that response from the 3 30 substrate in 1 mM ethanolic solution for ~16 hrs. These verification runs (denoted by triangles) were on the same line and performed very closely to expected performance. substrates were then rinsed thoroughly with ethanol and By fitting a plot of the square root of the dose versus dried in a stream of N. The substrates were then subjected response length, an equation was derived to correlate the briefly (15 s) to UV ozone treatment, then rinsed thoroughly measured dose from the response length of a sensor: 35 with ethanol and dried in a stream of N. The microstruc Furthermore, quality control criteria were developed dur tured substrate was then spin coated with 1 mL of 1 mM ing the development of embodiments of the technology. The ethanolic solution of lead(II) perchlorate. The micropillared sensors exposed to establish QC criteria were reasonably area of the substrate was then filled with ~3 microliter of LC consistent and a QC test window was established. E7:octane (40.60) mixture. A U-shaped polymer strip (~1 Based on experiments in which 11 exposures at 8 ppm for 40 mm wide) was patterned on another glass Substrate using 2 hours (16 ppm-hour) were recorded, an average response photolithography. The thickness of the polymer Strip was of 8.11 mm was measured. The sensors from the QC test maintained at 25 micron. This substrate was coated with were left at ambient (room) temperature for 6 hours after OTS and paired with the LC filled substrate to form a their HS exposure and then imaged again. The amount of head-space 20 microns thick head space. A U-shaped mylar response changed very little over the 6 hours indicating good 45 film was placed over the polymer Strip to generate micro response stability. These results indicate that (i) the micro fluidic cell with 45 micron head space. The substrates were fluidic cells can be used as cumulative dosimeters and (ii) held together using binder clips and three sides with the the total exposure dose can be calculated by measuring the polymer/mylar strips were sealed using low off-gassing length of the change in LC orientations. Using the algorithm epoxy to force the gas diffusion through the open end of the one can use these dosimeters to determine an unknown 50 sensor. These cumulative sensors, were stored in an argon concentration. environment prior to use. In addition, a microfluidic cell for measuring H2S was The cumulative sensors were then exposed to 1 ppm HS prepared and tested as a sensor for environmental monitor at 45% RH inside a smaller exposure chamber (9.5x7.5x4.5 ing. In these experiments, embodiments were tested that cm) at a flow rate of 5 L/min. The exposure chamber was were designed to detect lower concentrations of HS over 55 placed between two crossed polarizers and was flanked by a longer time periods of time, which is appropriate for envi CCD camera and diffused light source. The digital images of ronmental monitoring. In particular, the microfluidic cell the cumulative sensors were captured in real-time as the was tested under conditions appropriate for a device sensor was exposed to the HS gas. The captured images designed to detect approximately ppm-level concentrations were then analyzed to determine the length of the bright of HS during a typical work shift (e.g., for 8 to 12 hour 60 front as a function of exposure time using Image.J (NIH). exposures). FIG. 11 shows the variation of the response length as a Sensors were exposed to HS as described above and the function of the square root of the exposure time. The results minimum times needed for a response was recorded. In these show that the response length, after an initial delay, increases experiments, a response is defined as the first visually linearly with square root of the exposure time. And also detectable bright front observed on the sensor (typically -0.5 65 shows that the cumulative sensors with thicker head space mm in length). Data were collected for exposure to HS over height are more sensitive (shorter delay and higher response a range of 15 to 50 ppb. Responses were observed for HS length) than the sensors with thinner head space height. US 9,575,037 B2 55 56 These results again establish that the microfluidic cells can fluidic cells designed for cumulative measurement of gas be used for tuning the dynamic range of detection of analyte can be used for real-time detection. different gases. Example 6 Example 5 Microfluidic Cells for Cumulative Detection of Microfluidic Cells as Real-Time Sensors Formaldehyde During the development of embodiments of the present During the development of embodiments of the technol technology, experiments were performed to demonstrate that 10 ogy provided, experiments were performed to demonstrate the microfluidic sensors can be used as real time sensors. that the microfluidic cells can be used to detect HCHO The microfluidic cells were fabricated as described in (formaldehyde) using LC-based detection technology. In Example 4. These cells were then exposed to different this regard, first detection of HCHO was demonstrated using concentrations of HS at 45% RH inside the small exposure simple LC sensors. Next, microfluidic cells were fabricated chamber at 500 ml/min flow rate. The images of the sensors 15 using the LC and the micropillared Substrate to demonstrate were then captured in realtime using CCD camera. These that these cells can be used for cumulative detection of images were then analysed to determine the response length HCHO. (the width of the bright front). FIG. 12 shows the variation HCHO sensors were fabricated on patterned glass sub of the response length as a function of the square root of the strates decorated with polymer micro-pillars using conven response time. The results show that the response length, tional lithographic techniques. The array of micropillars after an initial delay, shows linear behavior with the square covered a 5 mm diameter area of the substrate. A droplet of root of the exposure time. The slopes of these straight lines LC (methoxybenzilidene butylanaline i.e. MBBA), when are different for different concentrations. These results indi deposited onto the array of micro-pillars was subjected to cate that measurement of the slope of these lines in real-time capillary forces that caused the LC to spread to form a stable can provide a basis for a real-time sensor using these 25 film. The pillar height (5 microns) determined the thickness microfluidic cells. of the film. These sensors were then exposed to vapors During the development of embodiments of the present generated by bubbling nitrogen (N) through the targeted technology, experiments were performed to demonstrate that chemicals. For example, HCHO vapor was generated by some modifications in the microfluidic cell format can lead bubbling N through HCHO in deionized water. The desired to detection of analyte with significantly shorter initial delay. 30 concentrations of HCHO were generated by diluting the Microfluidic cells were fabricated using the rectangular saturated stream with dry N. The HCHO concentration was micropillared area as described in Example 4 except after determined using a commercial HCHO detector (FP-30, filling the micropillared area with LC, the excess glass on RKI Instruments Inc.). the short side of the substrate extending to the edge of the The film of LC, when supported on the sensor surface, substrate was removed so that micropillared area extended 35 possesses optical birefringence and leads to a bright optical to the edge of the substrate. This substrate was then paired appearance of the sensor. Upon exposure to 17.5 parts per with another glass piece coated with OTS to form a ~45 million (ppm) HCHO, the LC changes to an isotropic liquid micron head space between the top surface and LC surface. with no optical birefringence and the sensor changes to a Two Substrates were then glued together along three sides dark appearance between crossed polarizers. A measurement using low-off-gassing epoxy. The microfluidic cell was then 40 of the amount of light transmitted through the sensor as a exposed inside the small exposure chamber (9.5x7.5x4.5 function of time provides the dynamic response of the sensor cm) at a flow rate of 5 L/min while its appearance was to HCHO. The sensor yields a measurable response to 17.5 captured in real-time using a CCD camera. The digital ppm HCHO (with 50% RH) in approximately 5 minutes images were then analyzed to determine the response length (FIG. 15). as a function of exposure time. FIG. 13 shows the variation 45 Furthermore, the data demonstrate the high selectivity of of the response length as a function of time. The results this sensor for HCHO relative to vapors from other chemi clearly show that with this cell configuration detection of 1 cals representative of alcohol and ketone groups. Using this ppm of HS is possible within 4 minutes of delay. sensor system, 7 ppm HCHO was detected in less than 30 During the development of embodiments of the present minutes. In addition, experiments measured the threshold technology, experiments were performed to determine if the 50 concentrations of toluene, hexane, benzene, and isopropanol microfluidic cells can actually be used to detect the change vapors required to induce a phase transition in a range of in the concentration of HS. LCs (e.g., MBBA, 5CB, E7, TL205, MLC-7800) to be A microfluidic cell with 20 micron head space was greater than 1000 ppm. Without being bound by theory, it is fabricated as described in Example 4 and sequentially believed that the response of MBBA to low ppm concen exposed to different concentrations 1, 2, 5, 1, and 2 ppm HS 55 trations of HCHO reflects, specific interactions between for 2, 1, 1, 1, 1, hours respectively. The HS concentrations HCHO and the 4-butylaniline, one of the components pres were maintained at 45% RH at a flow rate of 500 ml/min ent in MBBA. However, an understanding of the mechanism inside a small (9.5x7.5x4.5 cm) exposure chamber. The is not required to practice the technology. response of the microfluidic cell to the exposure was Experiments were performed to collect data demonstrat recorded in real-time and the images were analyzed. FIG. 14 60 ing use of the LC-based principles for cumulative detection shows variation of the response length as a function of the of HCHO. Embodiments of the technology were fabricated exposure time. The results show that the microfluidic cell (e.g., in the form of a cumulative dosimeter) and exposed to actually responds to the change in concentration of HS 7 ppm HCHO. The dosimeter was fabricated by using a 3.8 whether it is increasing or decreasing. As shown in the insets cmx1.9 cm glass substrate with a 3.5 cmx1.3 cm micropil of FIG. 14, the change in concentration can be detected 65 lared area. The micropillared area was filled with the LC within few minutes of the change in concentrations. These using capillary action to form a thin (5 micron) film. This results when combined together demonstrate that the micro sensor Substrate was then paired with a clean glass Substrate US 9,575,037 B2 57 58 with a head-space (e.g., a head space of approximately 45 corresponding to V, V, and 6 modes, respectively. In microns) to allow controlled diffusion of the targeted ana Some experiments, inverted peaks in the hydrocarbon region lytes above the LC film (FIG. 16a). When viewed between (2900 cm) indicated contamination of the reference gold crossed-polarizers, the dosimeter initially appeared bright Surface that was resolved by cleaning the Surface with a (FIG. 16b). The dosimeter was then exposed to 7 ppm butane torch. Once the FTIR spectrum was collected, the HCHO at a flow rate of 200 ml/minute for 8 hours. Dark Substrate was placed inside an exposure chamber and fronts appear in ~30 minutes and progress inward with time exposed to 3.5 ppm humid NO (50 sccm 4.7 ppm NO, and (see, e.g., FIG. 16b). As a result, the measured light intensity 20 sccm N bubbled through H2O) for approximately 30 decreases linearly with exposure time (FIG. 16c). The minutes. The FTIR spectrum of the exposed surface showed results demonstrate that exposure to HCHO leads to a phase 10 Some change in these three peaks, although no new promi transition of the LC that is evidenced as a dark front on each nent peaks were observed (FIG. 17). side of the dosimeter and that evolves as a linear function of Next, to test the ability of the instruments to detect the exposure time. The dark front moves linearly with cumula presence of ATP film on a 100 A thick gold film, experi tive exposure to HCHO (FIG.16c). Additionally, the fronts ments were performed with silicon wafers. A fresh (e.g., stay unchanged for days in an ambient environment, Sug 15 one-day old) gold coated silicon wafer was incubated in 1 gesting that these dosimeters provide a stable reading of mM ATP for ~16 hrs, rinsed with ethanol, and dried in a cumulative exposure over a typical (e.g., 8-hour) work shift. stream of N. Background spectra were collected from a Accordingly, these data demonstrated the feasibility LC piece of the same silicon substrate that was rinsed with based microfluidic cell to create a passive dosimeter badge ethanol and dried in stream of N. The peaks were well for toxic gases. The LC-based dosimeters are Small (~4 resolved and with the presence of Some background mois cmx2 cm), light weight (<5 g), and easily read by light ture (FIG. 18). intensity measurement to indicate cumulative exposure to an Experiments were performed to test the ability of SAGA analyte in the gas phase, e.g., HCHO. to resolve the FTIR spectra on 100 A gold deposited on a glass substrate. For these experiments, two fresh gold (100 Example 7 25 A) coated microscope slides were incubated in 1 mM ATP for ~16 hours, rinsed with ethanol, and dried in a stream of Channel-Based Analyte Sensor N. A background spectrum was collected from an identi cally prepared slide immersed in ethanol alone. The micro During the development of embodiments of the present scope slide was broken into two pieces. One half of the slide technology, experiments were performed to test devices 30 was used for FTIR experiments and the other half was used comprising a channel (e.g., a microfluidic channel) for use to prepare a LC cell. Analysis of the first halves of the slides in methods in which a functionalized surface in the channel showed that the FTIR peaks were well resolved (FIG. 19). is first exposed to an analyte and then the reacted function The SAM surface was also exposed to 3.25 ppm NO (100 alized surface is exposed to a liquid crystal for reading the sccm 4.2 ppm mixed with 20 sccm N bubbled through device. While the embodiments tested demonstrate the gen 35 water) for approximately 30 minutes. The film exposed to eral applicability of the technology, data were collected for NO showed a decrease in peak intensity and a small shift in an exemplary device comprising a gold Surface functional the peak positions (FIG. 19). These experiments demon ized with a self-assembled monolayer (SAM) of 4-amino strated that changes are detectable in the ATP monolayer on thiophenol (ATP) to detect oxides of nitrogen (e.g., NO or 100 A thick gold surface upon exposure to NO, (e.g., by NO, e.g., via conversion of NO to NO). A methoxyben 40 using FTIR). Zilidene butylanaline (MBBA) liquid crystal was applied to Alignment of Different LCs on ATP Treated Surface: the reacted ATP surface to measure the NO levels. After confirming the presence of an ATP monolayer using Some applications of gas monitoring relate to detecting FTIR (above), experiments were conducted to prepare an low levels (e.g., parts per billion) of gases. For example, ATP functionalized surface and evaluate the alignment of Some biomedical applications relate to detecting nitric oxide 45 liquid crystals on the Surface. (NO) gas in human breath for asthma monitoring. Detection To prepare ATP-functionalized surfaces, glass slides were of NO via conversion to NO, and detecting the NO, using cleaned by ultrasonicating for 10 minutes in detergent, then various compounds (e.g., Substituted aniline-based com rinsed in deionized water and washed in acetone and ethanol pounds) has been identified as one approach for detecting (reagent grade). A-2 mM ATP solution in ethanol (-68.4 mg NO. Among these approaches, ATP was identified as a 50 ATP dissolved in 200 ml ethanol) was prepared. Fresh gold substituted aniline compound for use in a NO detector. coated slides were incubated on clean staining dishes; one Experiments were conducted using a Fourier transform staining dish was filled with ethanol for reference and two infrared spectroscopy (FTIR) instrument equipped with a were filled with the ATP solution. Slides were incubated Specular Apertured Grazing Angle (SAGA) accessory to overnight, rinsed twice in 100% ethanol, and dried in N. detect functional groups present on a SAM Surface. In 55 before use. particular, experiments were performed to re-examine the To evaluate the alignment of liquid crystals on ATP ATP SAM, LC alignment on an ATP SAM coated surface, treated Surfaces, seven different liquid crystals having vary and detection of NO using these surfaces. ing physical properties were tested: Characterization with FTIR SAGA A SCB Glass slides coated with 1000 A gold were immersed in 60 ~ 1 mM ATP for ~16 hours. The substrates were rinsed with CTL-205 ethanol and dried in a stream of N. Using FTIR-SAGA, a D MLC-7800 background FTIR signal was acquired with a bare gold E MLC-6488 substrate that was soaked in ethanol overnight. The FTIR F MBBA (AeCO) spectrum of ATP SAM was collected using the background 65 G MLC-14200 (high Ae) spectrum as a reference. The ATP peaks were clearly visible A series of 1"x3" substrates were tested under the fol with three prominent peaks at 1480, 1590, and 1620 cm', lowing conditions: US 9,575,037 B2 59 60 1 incubated in ethanol ized Surface and NO gas was passed through the channel for 2 functionalized with ATP 10 minutes using a small needle at the end of the gas delivery 3 functionalized with ATP and exposed to NO system. The exposed Surfaces were then used to assemble 4 functionalized with ATP and exposed to N. LC cells by pairing them with OTS coated slides using 25 The substrates were cut into five pieces and paired with micron mylar as spacers. The LC cell was filled with MBBA OTS treated slides and lifter slips before filling the devices in isotropic phase at 50° C. NO concentrations of 88 ppb with a LC in nematic phase. The alignment of LCs on these and 50 ppb were generated by mixing 4.7 ppm NO, from a films was monitored for at least six days. certified cylinder (4.7 ppm) and humid nitrogen generated The results from these experiments show that 5CB aligns by bubbling nitrogen through DI water at appropriate ratios. homeotropically on a bare gold Substrate that was incubated 10 For negative controls, N, was bubbled through deionized in ethanol overnight (FIG. 20A). In addition, MBBA Water. assumes a homeotropic alignment on an ATP functionalized The results show detection of 50 ppb NO, by the ATP Surface and adopts a planar alignment on NO - exposed coated surface exposed along the path defined by PDMS ATP functionalized surface (FIG. 20B). In these experi channel (FIG. 23). The results indicate that measuring the ments, the other LCs tested did not show any significant 15 length of the bright path along the channel provides a means change in LC alignment upon exposure to NO, (FIGS. 20A to quantify the response of the chemically functionalized and 20B). Surface to an analyte. To ensure that the change in LC alignment upon exposure These results suggested that a longer channel having to humid NO was not from humidity alone, surfaces were controlled dimensions would provide a more precise and prepared and exposed to 3.5 ppm NO at 70 sccm (50 sccm accurate quantification of sensor response. Experiments 4.7 ppm NO, and 20 ppm N bubbled through water). were performed with PDMS channels prepared using an Identical Surfaces were also prepared by exposing them to aluminum master having a 1 mm widex1 mm thick ridge humid N. The results showed that the (i) ATP functionalized defining channel dimensions. To minimize the potential Surface can be used to achieve homeotropic alignment of LC variation during introduction of the gas, a small needle (~1 MBBA and (ii) LCMBBA can be used to report interaction 25 mm diameter) was integrated into the PDMS block with of NO, with the ATP surface (FIG. 21). channels (see FIG. 24). The ATP treated substrates were then Characterization of ATP Treated Surface: consistently placed over the PDMS channels and exposed to The previous experiments Suggested that a change different concentration of NO. Before exposure, the sub occurred at the ATP surface as a result of exposure to NO strate was firmly pressed against the PDMS block and a that can be reported by the LC MBBA. During the devel 30 weight was placed over the Substrate during the exposure. opment of embodiments of the technology, experiments After exposure, the PDMS channel was removed and the were conducted to characterize the surfaces using FTIR, exposed surface was paired with an OTS treated glass contact angle, and ellipsometric measurements. These Substrate forming a 25 micron cavity using a mylar spacer. experiments established the reproducibility of the function The two Substrates were aligned leaving a small lip along the alized surfaces prepared as described herein on 1000A gold 35 long edge of the cell to facilitate LC filling. The cell was and 100 A gold surfaces. For these experiments, the SAM secured and placed inside an oven at 60° C. LCMBBA was coated slides were first prepared as described herein and applied along the lip and allowed to spread inside the cell for then broken into two halves. One half was used for FTIR 5 minutes while the cell remained inside the oven. After 5 experiments and the second half was used for contact angle minutes, the cell was taken out of the oven and the LC cell and ellipsometric measurements for the 1000 A thick film. 40 was imaged at different time intervals starting from 2 FTIR spectra acquired of the ATP SAM were comparable minutes. to grazing angle IR spectra reported in the literature (see, Exposure experiments were performed with different con e.g., Langmuir 12 15 (1996) 3689). The spectra show a centrations and different equilibration times. The results decrease, especially at 1480 cm, in the peak intensity upon show that 25 ppb NO, is detected (FIG. 25). exposure to NO, (FIG. 22). FTIR spectra of ATP function 45 A number of experiments were performed at different alized Surfaces and Surfaces exposed to humid NO and concentrations ranging from 10 ppb to 80 ppb with a 10 ppb humid N are shown in FIG. 22. These results indicate that initial and then 20 ppb increments (FIG. 26). The images there are changes in the ATP surface upon exposure to NO from three different replicates were captured and analyzed 4 and the changes are not due to the presence of humidity. minutes after removing the cells from the oven. These Detection Using Channels: 50 results show that this method detects 20 ppb of humid NO The results of experiments performed during the devel after 10 minutes exposure with a resolution of 10 ppb. The opment of embodiments of the technology described dem results also show that measurement of the length of the onstrated that using a surface functionalized with ATP reacted channel provides a facile method to quantify the detects the presence of NO by using LC MBBA. Experi response as a function of concentration. The results also ments were conducted to verify that passing NO gas 55 show that there is a linear relationship between the length of through a narrow channel allows a faster reaction and the bright channel and the concentration (FIG. 26B.). therefore a sensitive detection with shorter response time Effect of Liquid Crystal Composition (e.g. 30 min). During the development of embodiments of the technol During the development of embodiments of the technol ogy, liquid crystal compositions other than MBBA were ogy, a polydimethylsiloxane (PDMS) channel was prepared 60 tested. MBBA has negative dielectric anisotropy (A630). to provide a well defined gas flow path on an ATP treated Since most of the materials tested previously had a positive Substrate. A "master” was prepared by gluing a ~ 1 mm wide, dielectric anisotropy (ASO), it was anticipated that LCs 3 inch long, and 0.7 mm thick glass piece on a 1 inchx3 inch with negative dielectric anisotropy might align homoeotro glass substrate using UV curable epoxy. A film of PDMS pically on ATP functionalized surfaces. mixture (prepolymer and curing agent) was overlaid on the 65 LCMLC-2080 and MLC-2081 (Merck), both with nega master and cured at 60° C. for 1 hour. The PDMS channel tive dielectric anisotropy, were tested. Both of these LCs was removed from master, overlaid on the ATP functional have a nematic-transition temperature above 80° C. ATP US 9,575,037 B2 61 62 treated Surfaces were prepared using the protocol developed with ATP were prepared and exposed to different concen herein. The substrates were broken into six pieces and paired trations of NO, at different flow rates. The LC cells were with OTS coated lifter slides. Two cells were then filled with fabricated and filled with pure MBBA and MBBA and MBBA, MLC-2080, and MLC-2081 in nematic phase. MLC-2080 at a 40:60 v/v ratio. The images of the LC cells Images were taken after 15 minutes to assess the alignment were collected 4 minutes after the cells were taken out of the of these LCs on the ATP coated surfaces (FIG. 27). The oven (FIG. 30). results suggest that MBBA aligns on the ATP coated surface The results show that pure MBBA is anchored strongly so that at 800 sccm, NO, could not induce the planar alignment (FIG. 27A) and that neither MLC-2080 nor MLC-2018 along the channel. The 800 sccm flow rate is too high and aligns homeotropically on the ATP coated surface (FIGS. could potentially induce leaks outside the channel so that the 27B and 27C, respectively). The homeotropic alignment 10 mixture adopts a planar alignment with 2 minutes of expo does not correlate with the dielectric anisotropy and it is sure to 10 ppb or 30 seconds of exposure to 20 ppb. The cells contemplated that the homoeotropic alignment of MBBA on detect 10 ppb NO after two minutes of exposure at a flow an ATP treated surface is due to the functional group present of 400 sccm. It is contemplated that cells that are resistant on MBBA. to leaking under high flows detect the presence of 20 ppb To determine the effect of mixing MBBA with another LC 15 after 30 seconds of exposure. having a negative dielectric anisotropy, MBBA was mixed Channel-Based Analyte Sensor with Higher Resolution with MLC-2080 at different volume ratios (pure MLC, 0.9 During the development of embodiments of the technol MLC, 0.8 MLC, 0.7 MLC, 0.6 MLC, 0.5 MLC, 0.25 MLC, ogy provided herein, a dose response curve for an analyte and pure MBBA: see FIG. 28 (a) through (h), respectively). gas was developed for a cell comprising a gold surface and The mixtures were vortexed, heated to 65° C. for 5 minutes 4-aminothiophenol. The cells were then applied to detect and Vortexed again. The mixtures were monitored over low concentrations of the analyte gas. several days to ensure that no phase separation occurred Test conditions were standard (see above) except that all over time. NO concentrations were equilibrated overnight and a 35% Two identically prepared ATP functionalized surfaces MBBA/65% MLC-2080 liquid crystal mixture was used. were broken into 8 different pieces. Each piece was then 25 Concentrations of NO tested were from 10 to 40 ppb in 5 paired with a piece from an OTS coated glass substrate, thus ppb increments and 40 to 100 ppb in 10 ppb increments. forming a 25 micron thick LC cell. One cell each from each Controls were 0 ppb NO and pure nitrogen. The LC cells slide was then filled with the LC mixture at 60° C. inside an were exposed to different concentrations of NO, imaged oven after equilibration for 2 minutes. After 2 minutes of (FIG. 31), and analyzed by measuring the total distance of equilibration, each cell was filled serially inside the oven. 30 continuous LC disruption. The measurement of the length of After 5 minutes, the oven was closed and the cells were LC disruption was performed using Software, e.g., by over equilibrated for another 5 minutes. The LC cells were laying the image with a technical drawing of the channel imaged in the order they were filled. Images were taken after marked with hash marks in millimeter increments. The another 5 minutes of annealing at 60°C. The results suggest extent of continuous LC disruption in the cells was matched that the mixture of MLC-2080 and MBBA aligns homeo 35 with the drawing to determine the length of the phase tropically on an ATP treated Surface at a concentration as changed path. high as 80% (FIG. 28). The incubation time inside the 60° The results show that low amounts of NO (e.g., ppb NO) C. oven needed to achieve homeotropic alignment increases are detected. A linear relationship exists between the NO. with increase in MLC concentration. These results indicate concentration and the length of the bright channel on the that mixtures of LCs provide, in some embodiments, better 40 surface functionalized with ATP (FIG. 32). sensitivity to NO, than a single LC (e.g., MBBA) alone. Conclusions To confirm this result, identically prepared ATP coated In sum, these experiments demonstrate that ATP function surfaces were exposed using the PDMS channel to 20 ppb alized surfaces promote a homeotropic alignment of MBBA NO for 5 and 10 minutes, and they were then filled with and a MBBA/MLC-2080 mixture of up to 80% of the MLC pure MBBA or a mixture of MBBA and MLC-2080 at a 45 component. The time it takes for homeotropic alignment 40:60 V/v ratio. Optical images were acquired of the cells increases with an increase in the MLC concentration and fabricated using surfaces exposed to 20 ppb NO, and filled decreases with an increase in incubation temperature. The with different LC mixtures (FIG. 29). The images were taken homeotropic alignment can be obtained with an ATP surface after 10 minutes of equilibration at ambient temperature alone without a need for a top OTS treated surface. The ATP after removal from a 65° C. degree oven. The results show 50 functionalized surfaces, when exposed to NO, promote that 20 ppb NO is detected using pure MBBA after a 10 planar alignment. The change in the ATP Surface was minutes exposure (FIG. 29(a)). The surface exposed to 20 verified by FTIR in the form of a decrease in the peak ppb NO for 5 minutes and using pure MBBA does not give intensities corresponding to the C C and N—H stretches. any measurable response (FIG. 29(b)). However, the mix A micro fluidic channel provides a method to quantify the ture of MBBA and MLC-2080 at a 40:60 v/v ratio provides 55 response to NO by measuring the length of the reacted path a measurable response after 5 minutes of exposure (FIG. of the channel as reported in the form of the planar align 29(c)). The data show that (i) a longer exposure time gives ment of the LC. A higher flow rate combined with the more time for NO to react and therefore provides a greater MLC-MBBA mixture detected 10 ppb NO at high humidity measurable response and (ii) sensitivity of detection can be with 2 minutes of exposure. improved by using MBBA-MLC2080 mixtures. 60 Effect of Flow Rate Example 8 Experiments described above demonstrate that using the mixture MBBA and MLC-2080 at a 40:60 v/v ratio detects Identification of Surface Composition for Organic the presence of 20 ppb NO after a 5 minute exposure at 100 Vapor Detection Using Liquid Crystals sccm. Next, experiments were performed to determine if 65 increasing the flow rate improves the sensitivity of detec During the development of embodiments of the technol tion. To test the flow effect, identical surfaces functionalized ogy provided herein, experiments were conducted to iden US 9,575,037 B2 63 64 tify surface combinations for detecting VOC (e.g., toluene which will be influenced by factors such as relative polari vapor) with a liquid crystal (LC). In particular, data were ties, polarizability, and hydrogen bond-donor/acceptor prop collected from testing combinations of a substrate and a erties of the LC and analyte (see, e.g., S.J. Patrash and E. liquid crystal Suitable for determining an unknown concen T. Zellers (1994), “Investigations of nematic liquid crystals tration of toluene in the vapor phase. Several physical 5 as Surface acoustic wave sensor coatings for discrimination characteristics of the LC were monitored as indicators of between isomeric aromatic organic vapors'. Analytica Chi VOC concentration, including LC phase transition, LC mica Acta 288: 167-177). Perturbation also depends on the orientation change induced by change in the structure of shape (rod-like or planar) of the analyte. For example, polymer film due to Swelling, and dissolution of toluene arene-arene interactions between Substituted aromatic Sol soluble materials into the LC to initiate LC orientation 10 change. Although particular experiments described herein utes (dopants) and an aromatic liquid crystal Such as 4'-pen are focused on toluene detection, similar embodiments com tyloxy-4-cyanobiphenyl (5OCB) induce perturbations in the prising combinations of Substrate and LC are appropriate for bulk properties of the liquid crystal phase (V. E. Williams detecting other volatile organic compounds. and R. P. Lemieux (1998), “Role of dispersion and electro static forces on Solute-solvent interactions in a nematic The experiments used LC materials that comprised rod 15 shaped organic molecules such as cyano-biphenyls (e.g., liquid crystal phase'. J. Am. Chem. Soc. 120: 11311-11315). 5CB (4-cyano-4'-pentylbiphenyl) and E7 (a liquid crystal As such, experiments were conducted to confirm that intro mixture comprising several cyanobiphenyls with long ali ducing an aromatic dopant (e.g., a VOC Such as toluene) into phatic tails). These molecules form condensed phases that the aromatic LC host (e.g., 5CB) causes a shift in the possess crystal-like long range orientational ordering but nematic-isotropic transition temperature that is a function of lack positional ordering. The long-range ordering of mol dopant-host interactions. ecules within the LC gives rise to anisotropic optical prop During the development of embodiments of the technol erties that result in a bright or dark appearance of the LC ogy provided, experiments were performed to evaluate two when viewed between crossed polarizers with a backlight different LCs having different physical and chemical prop source. Experiments were performed to confirm that toluene 25 erties and to determine their effectiveness for detecting vapor causes a change in the polymer Surface Supporting a toluene and other organic vapors. The sensors fabricated for thin film of LC, e.g., due to polymer Swelling or due to these experiments comprised a micrometer-thick film of LC dissolution of the polymer surface material into the LC (5CB or E7) supported on a glass substrate decorated with exposed to toluene. Both these phenomena induce a change polymeric micro-pillars (5 um tall, 10um diameter, 20 um in the LC orientation on the surface that can be easily 30 detected by monitoring a change in incident light intensity. center-to-center spacing). The micropillars are used to form For example, absorption of toluene directly into the LC mechanically robust thin films of the LC. The sensors were phase disrupts the long-range order of the LC, thus giving exposed to toluene or other organic vapor using an in-house rise to a phase transition to an isotropic material and gas exposure system schematically shown in FIG. 40. The producing distinct changes in the optical appearance of the 35 exposure system consists of a gas delivery system (mass LC (see, e.g., E. J. Poziomek, T. J. Novak, and R. A. flow controllers, gas dilution system, etc.) and an optical MacKay (1973). “Use of liquid crystals as vapor detectors'. image capture system (diffuse light Source, CCD camera, Mol. Cryst. Liq. Cryst. 27: 175-185). polarizers, etc.). The Saturated vapor of the target analyte FIG. 33 shows the basic principle of toluene detection was generated by bubbling Ngas through the liquid analyte. using LC phase transition. A sensor comprising LC Sup 40 The Saturated vapor analyte is then diluted at an appropriate ported on a Substrate with polymeric micropillars on a glass ratio to generate the desired concentration before delivering substrate initially appears bright (FIG. 33B, left). Upon it to the exposure chamber that houses the optical cells exposure to toluene vapor, the LC material undergoes a (sensor) prepared with the combination of substrate and LC. phase transition and the sensor appears dark (FIG. 33B, This gas delivery system was used to deliver a range of gases right). The pre- and post-exposure appearance of the LC 45 at various concentrations from the ppb to the ppm range. The sensor depends on the Surface upon which the LC is depos sensors are placed inside an exposure chamber that is ited. For example, a LC Supported on glass Substrate with connected to the gas delivery system and flanked by two polymeric micropillars (e.g., FIG. 33) initially appears crossed polarizers. The chamber is placed between a CCD bright and turns darker upon exposure to toluene while LC camera and a diffuse light source for real-time quantitative Supported on a polymer or other materials spin coated on a 50 measurement of the optical change in the sensor. glass Substrate (e.g., as disclosed below) initially appears Prior to exposure to toluene or other vapors, the LC dark and becomes brighter as toluene causes a change in LC possesses a bright appearance when viewed through crossed orientation due to polymer Swelling or due to a change in the polarizers with a backlight source. When the sensor was original Surface. exposed to a known concentration of the targeted analyte, LC Phase Transition 55 the analyte diffuses into the LC film and lowers the isotropic LC phases form as a consequence of intermolecular transition to approximately room temperature. This expo interactions that stabilize the long range orientational order Sure induces a nematic-to-isotropic phase transition when a ing of molecules within the LC phases. These interactions threshold concentration of analyte is reached (e.g., see FIG. can vary Substantially (e.g., arising from dipolar or Steric 33). The phase transition in the LC causes a striking change interactions, dispersion forces, or hydrogen bonding) and 60 in the optical appearance of the sensor. FIG. 41 shows a LC depend on the structure of the molecules comprising the LC. sensor (5CB) that was exposed to 5000 ppm toluene vapor. When the LC material is exposed to an organic vapor Similar LC sensors exposed to either dry (RH 0%) or humid analyte such as toluene, the analyte partitions from the vapor (RH 95%) nitrogen alone didn't show any detectable into the LC and thereby perturbs the LC ordering, thus changes. The toluene-induced changes of the LC are revers providing a measurable property of the sensor's response. 65 ible—removing the vapor Supply restores the original bright As such, the extent of the perturbation induced by the appearance of the LC film. The sensor responses to toluene analyte in the LC depends on the analyte-LC interactions, and other organic solvents are summarized in Table 3. US 9,575,037 B2 65 66 TABLE 3 The sensor response discussed above requires a very high concentration of toluene to yield a visual change. A higher Organic solvent concentrations required to induce a phase transition in two sensitivity can be obtained by: i) measuring the vapor different LCS (SCB and E7 response closer to the LC isotropic transition temperature, ii) analyte 5CB concentration E7 concentration choosing LCs with a lower isotropic transition temperature, benzene no change up to 20,000 ppm NA and iii) using a sensitive instrument that will detect the toluene 5000 ppm 11,000 ppm signal (e.g., the optical properties) prior to the formation of m-xylene 1500 ppm NA isotropic phase. nitrobenzene NA 200 ppm Polymer Based Detection hexanes no change up to 10,000 ppm NA 10 Aromatic hydrocarbons (e.g., toluene) are known to Swell isopropyl alcohol 7500 ppm NA formic acid 20,000 ppm NA various polymers. This effect is particularly pronounced for methanol 80,000 ppm NA polymers of vinyl and styrene moieties (see, e.g., P. Muller buschbaum, et al. (2006), “Fast swelling kinetics of thin polystyrene films, Physica B, 385-386,703-705; B. Pejcic, The data in Table 3 shows the relative sensitivity of LC 15 etal (2007), “Environmental monitoring of hydrocarbons; A sensors towards different organic solvents. These data Sug chemical sensor perspective', Env Sol & Technol. 4(18); gest that the LC sensors made with 5CB and/or E7 are 6333-6342). LC orientation on a surface is extremely sen relatively more sensitive to aromatic solvents than non sitive to the physical and chemical changes that occur at the aromatics (except for benzene). This is perhaps due to LC-Surface interface, thus the Swelling property of polymers favorable L-L interactions between aromatic solvents and 20 surface provides a basis for developing LC-based toluene cyanobiphenyl LCs. The data in Table 3 also indicated that sensors. Several polymers were identified (Table 4) based on 5CB was more sensitive than E7 due to its lower nematic the knowledge that these polymers Swell upon toluene isotropic transition temperature. exposure. TABLE 4

Exemplary polymers

Polymer Properties

Poly(vinyl acetate) Average MW ~100,000; (PVAc): transition temp: Tg: 30° C.

Polystyrene (PS) Average Mw -280,000; transition temp: Tg: 100° C.

Polystyrene Average MW -9500; Low-MW PS transition temp: NA

Polyisobutylene Average MW ~500,000; PiB) transition temp: Tg: -64° C.

HC CH pi US 9,575,037 B2 68 TABLE 4-continued

Exempl olwmers Structure Polymer Properties CF3 SC-F103 NA HO (Seacoast Science Inc.) FC l

CF CH CF

The selected polymers (Table 4) were screened for their addition. Although the exact reason for this rubbing-induced activity with toluene (e.g., at concentrations in the range of LC alignment is not yet understood clearly, the technique is 1000 S of ppm) using liquid crystal optical cell by pairing used very often to align LCs on different polymer surfaces two glass Surfaces to Support a thin film of LC. The polymers (Wu, et al. (1996) “Liquid-crystal alignment of rubbed were deposited onto the clean glass Surface by spin coating. 25 polyimide films: A microscopic investigation'. Applied The detection of the polymer surface response to the toluene Physics B. Lasers and Optic, 62(6), 613-618). vapor was conducted in two different ways. In the first one, FIG. 42 shows microscope images of cells prepared with a polymer coated Surface was first exposed to a known the rubbed or unrubbed polystyrene films and E7 viewed at concentration of toluene vapor followed by measuring the different orientations of the cell with respect to the cross intensity of light passing through an optical cell made by 30 polarizers. FIG. 42b shows a change in light intensity (e.g., combining the exposed polymer-coated Surface, LC (E7), from dark to bright) through the optical cell made with and an OTS-coated glass slide. The intensity of light passing rubbed polystyrene film when the cell was positioned at 0 through these optical cells was measured by using a polar and 45 degrees with respect to the crossed polarizers. This ized microscope equipped with crossed polarizers and a change indicates a homogeneous planar alignment of the LC backlight source. A change of light intensity transmitted 35 on the rubbed polystyrene surface. Similar rubbing-induced through the cell prepared with the exposed surface due a LC homogeneous alignment was observed with PVAc, PiB, and orientational change was compared with a cell made with an SC-F103. Quite unexpectedly, the surface prepared with low unexposed surface. In the second method, an optical cell that MW PS from a 15 mg/ml toluene stock solution showed was made by a combination of a polymer-coated Surface, LC homeotropic alignment without any rubbing (FIG. 42c). As (E7), and an OTS-coated glass slide was monitored for a 40 this surface aligned LC (E7) homeotropically with or with change in the light intensity transmitted through the cell out rubbing they were not further tested with toluene. placed between crossed polarizers. Mean gray-scale inten However, the same low MW PS was used to test the sity (MGSI) was measured as a function of exposure time dewetting induced orientation of LC (see below). using a CCD camera and backlight Source. For toluene exposure studies, a series of optical cells were Polystyrene 45 prepared using mechanically rubbed PS substrates coated on The liquid crystal alignment properties of the polystyrene glass, an OTS-coated glass slide, and E7. The cells were coated films were tested with glass-OTS sandwich optical exposed to nitrogen or toluene and images were collected at cells. Glass slides (Fisher finest: plain premium microscope a regular time interval using the experimental set up shown slides) were thoroughly flushed with nitrogen (N) and then in FIG. 40. The results of exposure experiments are sum rinsed thoroughly with ethanol and acetone. Slides were 50 marized in FIG. 43. The data in FIG. 43a show that there initially dried with N followed by heating at 100° C. for 30 was no change in the overall planar alignment in the LC cell minutes. Slides were further UV-ozone cleaned for 5 min due to toluene exposure when viewed under the microscope. utes. All glass slides used in this study were cleaned with this However, the data in FIGS. 43b and 43c show a definitive same procedure. The glass slides (1"x1") were coated with change in the LC cells due to toluene exposure when 100 ul of 15 mg/ml stock solution of the polymer polysty 55 compared to the cell exposed to nitrogen alone. A similar rene dissolved in toluene. In this sandwich optical cell, an change of a smaller magnitude was observed when the LC OTS-coated glass slide and a polystyrene-coated glass slide cell was exposed to 2900 ppm toluene vapor. were aligned facing each other. The two surfaces were kept In another test, a PS coated surface was used where the apart by a spacer having a thickness of ~30 Lum. A 10-ul drop polymer Surface was first exposed to a known concentration of LC (E7) in nematic phase was placed at the center of the 60 of toluene vapor followed by measuring the intensity of light polymer-coated glass piece, then the OTS-coated glass piece passing through an optical cell made by combining the was put on top of it. The two surfaces, having a spacer and exposed polymer coated surface, LC (E7), and an OTS LC in between them, were held together using binder clips. coated glass slide. A series of glass Substrates were coated The LC optical cells were imaged using a polarizing optical with PS films, the surfaces were mechanically rubbed, and microscope. A homogeneous alignment of E7 on the poly 65 then exposed to toluene. After toluene exposure, the Surfaces styrene was induced by rubbing the polymer coated Surface were overlaid with LC (E7) to prepare an optical cell for with a velvet cloth in one direction for five times before LC measurement. A sandwich cell prepared in this manner was